Perfectly fine to keep it all green. That was Robbie's advice to me when he rebuilt mine in 2012. 125,000 miles and 10 years later, all is well. GX and 100 had red, they are both now pink. Pink and red are compatible. Flame suit on!The plan is to fill the cooling system with distilled water, as it had green coolant in it when I took everything apart, and fill and drain it until everything runs clear, then fill it up with Toyota red. I'm not worried about sludge because everything was nice and green.