This might sound oversimplistic, but if the red dye came off the t-shirt when it was washed in water, wouldn't it make sense to try soaking the grey track suite in warm water to get that dye back into solution in the water.
I'd try soaking the track suit in warm SOAPY water and see if the water starts to turn pink.
But, before you do that, try dampening a white tissue with some nail polish remover and dab the grey track suit and see if the white tissue starts to turn pink where it's being dabbed. If so, then the dye is soluble in a strong solvent like acetone, and you could probably remove the dye by dabbing it off with acetone (or even pouring some acetone in a shallow pan, dipping the grey track suit and then rinsing off that wet area of the track suit in running water). Acetone is soluble in water. So, if you can dissolve the dye in acetone, and then flood the acetone with water while the dye is still dissolved in it, that would remove the dye.
If both of the above fail to remove the dye, then try asking these people:
http://www.ritdye.com/
RIT makes clothing dyes that are sold in clothing and grocery stores across North America. I expect they have been asked how to remove dye more than once.
And, if they have no answers, I'd soak the track suit in water and add a small bit of bleach and agitating. The idea here is that if there's only a little pink on the track suit, if you can use the bleach to remove just as much pink dye as you do grey dye, then you'll be left with a lighter shade of grey (with no pink in it) which may be more acceptable to your son.
And, if all else fails, then dye the track suit another color. See the RIT web site for detailed instructions on how to do that. The describe a dry stove top method for dying clothing a very dark color, like navy blue or dark brown that would cover up any lighter color.