The red is only a dye. Automatic transmission fluid is red, regular coolant is green, long-life coolant is orange, and they are all that color because of the dye used. Base oils or ethylene glycol is close to clear in color, perhaps a little amber; additives are from honey to tan in color.
Color will not tell you about additive content; automatic transmission fluid is not highly treated and is red; engine oil has more "stuff" and, for example, Quaker State has a clear bottle to show their oil is nearly colorless. Diesel engine oils have upwards of 20% additive (a true high performance oil) and are not necessarily dark.
As for the 20W50 vs 5W50: The "W" number is generated from two low temperature tests- think of 1) stirring a milkshake and 2) sucking the milkshake through a straw. As oil gets cold, it gets harder to stir; at some temperature it will start to turn solid and you won't be able to **** it through the straw. While the synthetic and mineral oil will both get thicker and thicker as they are cooled down (and harder to stir), a synthetic oil will not turn solid until a far lower temperature than the mineral oil. However, it is still hard to stir, and so that becomes the limiting feature and it receives the "thicker" 20W rating.
You can't label a lubricant as a particular viscosity grade like a 20W-50 and not have it be such. There are long standing API viscosity grade categories to define both the low and high temperature characteristics of an oil with both upper and lower viscosity limits; an oil will fit only into one of those at a time. Further, as the performance testing for engine oils becomes more complicated, different viscosity grades are used for the different tests, so testing one grade and then claiming it's another is shady, too.
