Instead of answering them individually, I'm going to give my best explanation here.
WHAT WE KNOW ABOUT COLORS:
1. Colors are not "absolute ratings" - they are "derivative ratings" that are affected by a player's underlying attributes. A player's "Current" and "Future" Rating are calculated based on their "Current" and "Potential" attributes respectively ("Athletic" attributes with no "Potential" rating apply to both).
2. This "Derivative" rating is changed into a "Color" for presentation by FBB. The colors used are arbitrary and can be changed within the game (though we use the default).
Tier 6 (Purple) = Rating of over 150
Tier 5 (Blue) = Rating between 115 and 150 inclusive
Tier 4 (Green) = Rating between 100 and 114 inclusive
Tier 3 (Yellow) = Rating between 80 and 99 inclusive
Tier 2 (Orange) = Rating between 60 and 79 inclusive
Tier 1 (Red) = Rating of less than 60
3. The exact function used to derive these ratings is not known (believe me, I have tried to reverse-engineer it). Here are things I "know:"
- Three-Point Usage is not factored into the "Current" and "Future" ratings.
- Fouling is not factored into the "Current" and "Future" ratings.
- Injury Avoidance is not factored into the "Current" and "Future" ratings.
- Attributes do not affect Current and Future ratings linearly (i.e., doubling an attribute may not double its contribution to the Rating)
- Some attributes are tied to other attributes when calculating rating (e.g., Perimeter Defense and Quickness are "tied together" - a player with a higher Quickness sees a higher Rating increase when the Perimeter Defense attribute is raised than a player with a lower Quickness rating).
On the left is "J.R. Smith" as his attributes appear in a new (test) league created in 2012. Note that his "Current" rating is 112 (green) while his "Future" rating is 115 ("blue"). On the right is a New Player created in a test league that is in the 1980 season. Note that everything about the player's Attributes (except his birth year, normalized to make his age the same, and his last name, containing the year for ease of distinction) is absolutely identical. In 1980, those exact same attributes give him a "Current" rating of 118 ("blue") and a "Future" rating of 121.
CONCLUSIONS:
Stop. Worrying. About. Colors. They are just the output of some arbitrary formula which nobody understands and which the creator of the game chose never to reveal. The formula tends to, but does not always, accurately reflect how a player will perform, and given it ignores some ratings (especially Fouling) it is prone to some significant blind spots (your purple/purple with a 0 foul rating is never actually going to be a superstar because he's never going average more than 18 minutes per game - he'll foul out first). Use them as a shorthand to quickly comprehend a roster, but they're not gospel and you shouldn't feel a player "needs" to be of a certain color.
(As a specific example from last season, check out David Thompson Archives/NPBSL/1980/players/player308.htm and World B. Free Archives/NPBSL/1980/players/player129.htm - the only noticeable difference in their ratings is that Free has a higher INS and PAS rating, but they're almost identical everywhere else - and except for assists, their stats ALSO look almost identical despite Thompson being green/green and Free being blue/blue.)
Also, be aware that a player "on the border" of a color (e.g., with a 115 rating and showing as blue) might "lose" a color the following year even if his attributes remain completely unchanged as the game's expectation of what is "normal" in the league changes... and don't freak out about it.
Finally, note that Tier 5 ("Blue") encompasses a much broader range of players than any other range. A "low end" blue player is closer to a "yellow" player than a "low end" green player is to an "orange" player. This means "blue" especially cannot really be trusted to give you an accurate assessment of a player's capabilities.