I put G/Y/R just to be safe, but Leme test it real quick
EDIT: Nope. Just from green and leads to red. I'm guessing you need a Red Axe to get a fully charged FC [b+D] to link 5A > 2B, and if you do it from grey, your only at Green by the time you get to [b+D], and at Yellow if you start from Blue. Might be other ways using the same idea, though. Worth testing. Going from grey to red off a 5a poke is definitely worth 25 heat.