is there any way to set specific colors for traffic?

Indeed, there is a way! While traffic is running, open the console with tilde (~) and enter this in:

Code:

for k, v in pairs(gameplay_traffic.getTrafficData()) do v.paintKeys = {"Pearl White", "Jet Black"} end

The colors work as paint names, so if the vehicle doesn't have it, it might not work.

Here is another example that gets all red colors and checks for them (make sure that traffic is fresh, though):

Code:

for k, v in pairs(gameplay_traffic.getTrafficData()) do
  local new = {}
  for _, p in ipairs(v.paintKeys) do
    if string.find(string.lower(p), "red") then
      table.insert(new, p)
    end
  end
  v.paintKeys = new
end