What you think you know about the differences is probably wrong, simply because it's based on anecdotal thoughts and observations, not scientific fact.
"Cannabaceae is a small family of flowering plants. As now circumscribed, the family includes about 170 species grouped in about 11 genera, including Cannabis (hemp, marijuana), Humulus (hops) and Celtis (hackberries). Celtis is by far the largest genus, containing about 100 species.
Species in the genus cannabis are cultivated for medical or recreational use as marijuana, primarily the sativa and indica species. Several selectively bred "strains" have been produced for higher yields of THC and other cannabinoids, as well as terpenes with desired flavors, such as blueberry
Cannabis is Hemp -- Hemp is Cannabis, and all strains in this species are under this Genera -- Cannabis/Hemp.
Cannabis -- whether it is referred to as Hemp, Cannabis, Sativa, Indica, Ruderalis, etc., -- they are all just complex systems that manufacture a detailed blend of chemicals -- yes, CHEMICALS -- it's ok -- the word won't hurt you -- everything around us is made up of chemicals -- we have biological systems that produce compounds and hydrocarbons -- whether they are terpenes, gases or more complex compounds such as cannabinoids, etc. -- they are all produced using the building blocks of simple elements on the periodic table -- chemicals.
When it comes to getting high on marijuana, the conventional wisdom (incorrect, for the most part) is that one of two species of the plant—cannabis sativa or cannabis indica—will determine whether you get an up high or you get a knockout high. A third "species", cannabis ruderalis, has also been identified, but it doesn't have much psychoactive effect and is more hemp-like -- hemp is defined by it's THC content, or lack-of -- period.
There is a bit of truth to this, of course -- how are legends created...? Indicas can produce stuporous, narcotized highs, while sativas can produce giddy, exhilarating ones—but there's a LOT more to it than that. And those relying on the good old sativa = up / indica = down as a guide will find themselves in for a very rude awakening -- this just doesn't hold true -- it's a truth based on feelings and observations, rather than fact.
Typically, whatever strain someone "cut their teeth" on -- the 1st to 5th time someone uses Cannabis, whatever cannabis strain they opt for (usually their older brother/sister's stash, or something someone got their hands on somehow), THAT'S the strain they will base their opinion on FOR-EVER...! If it is purple, and they don't like the way it made them feel, they will NEVER like purple cannabis -- just because of the associative color -- not because the "purple" made a bit of difference -- the first experience sets in stone forever the strain of their preference.
The differences between the two species are evident to the naked eye. Sativas typically are tall and lanky, with long narrow leaves, while indicas are shorter, stouter, bushier, and have thicker, stubbier leaves. That is because the two cannabis species developed in different environments.
Marijuana's origins are in South and Central Asia, and that the plant differentiated itself into distinct species to accommodate different humidity regimes. The thin, lanky stems and long leaves of sativa plants allow the plant to respirate more efficiently and prosper in high humidity, while short, squat indicas evolved to deal with hot, dry conditions.
Thus, landrace varieties — "pure" original strains of indica, such as Afghani and Hindu Kush— developed in the dry foothills of the Himalayas, while pure sativas evolved in humid lowlands and river valleys. But in the US market today, landrace strains are a rarity. The vast majority of the Cannabis grown and consumed in the US is one indica-sativa hybrid or another.
The differences come in the physical appearance of the plants and types of chemicals they manufacture, in different ratios and and blends. These are determined by a myriad of influences, the main one being the environment in which it is grown, and the stock from which it comes from. If seeds from a plant that was grown in the hot, wet, deep jungles of Africa or South America was planted in the dry climate of say, Afghanistan or Morocco, that plant would have a hard time surviving, as it is used to a hot wet climate as well as 4-6 month summers, not the 2-3 month summers of the hotter, drier climate.
Over thousands and thousands of years, the leaves of the plant stock grown in Morocco became much fatter, and stature short and squat, so as to mature fast enough to make seeds and complete it's growth cycle within that 2-3 month window of summer -- Indica -- a subspecies of Cannabis. The leaves of the Sativa grow long and slender, and mature much more slowly, because of the much longer season -- they grow very tall and don't have to compete with the shorter plants for light -- also a subspecies of Cannabis.
For growers, even if they want characteristics of a specific Sativa, they don't want to spend extra weeks waiting for it to mature, so they use hybrid strains with varying amounts of Indica that will ripen faster than a pure Sativa.
But you won't always get the high you think you're going to get. That's because growing conditions make a difference, and even stabilized strains, pure or hybrid, can exhibit new traits when grown in conditions to which they are not accustomed. But part of the reason is a bit stranger—and calls into question the traditional reliance on the indica/sativa distinction.
The terms sativa and indica are only really valid for describing the physical characteristics of the cannabis strain in a given environment. They are not reliable as terms for making assumptions about energy/clarity versus sleepy/soporific.
The effects of THC, whether in indicas or sativas, are the same: It creates a euphoric, uplifting sensation when smoked or vaporized. That sound pretty much like what traditionally is known as a sativa high, so if indica contains THC just like sativa, why do some Indicas (and many Sativas) leave you in stupor?
While both indicas and sativas generally contain a full complement of cannabinoids in addition to THC, and many of the same terpenes—chemical compounds that create odors and essential oils—some are especially heavy in terpenes that modify the up THC high. One of those influential terpenes is myrcene.
Myrcene is one of the more common ingredients responsible for modifying the normal energetic effect of THC into a soporific effect.
Myrcene and other terpenes, as well as other cannabinoid ratios rather than THC are probably the most important variables in creating the psychoactive differences between strains -- NOT determined by whether the strain is a Sativa or Indica -- but more drawn along the lines of what combinations of Terpenes, Cannabinoids, Flavenoids and other chemicals are shared in the same ratios.
This is really referred to as the "entourage effect," which is the combination of different cannabinoids and terpenes working together that creates the distinctive highs of various strains.
Myrcene and most other terpenes aren't limited to Cannabis. They exist in many fruits and plants around the world, and are responsible for mood-altering effects in a myriad of instances and plants.
The warm, relaxed feeling when you consume beer -- that effect is, to a good extent, due to the myrcene present from the hops.
Also from Wikipedia:
"Beta-caryophyllene was shown to be selective agonist of cannabinoid receptor type-2 (CB2) and to exert significant cannabimimetic antiinflammatory effects in mice. Antinociceptive, neuroprotective, anxiolytic and antidepressant  and anti-alcoholism activity have been uncovered."
Beta-caryophyllene is also in hops, and could be responsible for some of the effects mentioned above when consuming beer.
Myrcene and the rest of the terpene levels make a difference in the feeling produced -- a level below about a half a percent doesn't seem to effect the "upness" of the high.
Strains available (ACDC is a perfect example) of Sativa that begin to produce a sopophoric feeling at about 1% or more myrcene, and yet it is CBD-dominant, with very little THC. A few strains have a myrcene content in excess of 3%. Other chemicals may well play minor roles in the more stony/sleepy effect, including CBD (when combined with THC and myrcene), CBN and linalool, when they are present in strains, as well.
Also, the color of the plants vary from plant to plant depending on environment, growing conditions, nutrient content of the soil and temperature variances, and strain-to-strain, but have no bearing on effect.
In closing, the CBD-to-THC-to-THCv-to-CBG-to-CBN ratios, as well as the Terpene ratios -- that is what determines all of the medicinal attributes, characteristics and effectiveness of this amazing plant -- not whether it is a Sativa, or an Indica.
There we go:
The Cannabis plant Effects and Attributes according to Fred DeLisio, HHS Associates.