Hi Sergi. Do you mean this number here?
If so, the colour is just an indication of how developed you are in that area.
Red = Weak,
Grey = Average,
Green = Strong.
The colour used is only related to the best possible car for your tier (the example above is in elite so can be developed up to 200 DP) and nothing else, so serves little purpose bar looking good and making your strengths easy to see.
Tigg
"If the number is grey it means you have the equal or best in that area, change focus to another area...."
I believe (I may be wrong, hence checking what OP is asking about) that the late mention of research has caused you to slightly misunderstand the question. Everything is exactly as you say if a research box turns
red instead of green.
Note: Sergi, research gains depend on the difference between your car and the best in that area, so following Tigg's advice for research will likely be helpful too :D