it makes fook all differance as the heat inside your intercooler will always be hotter than ambiant, and its also force-cooled , if you wanted to 'warm up your cooler then you owuld paint it black as black absorbs heat (aslong as the ambiant is hotter than the cooler ) if you wanted to remain a cool internal temp from higher ambiants then you would have a silver or bright colour to reflect the ambiant (being higher than the internal temp) which all of the above never is or we wouldnt be running intercoolers !

- i thank you