Canary blennies are brighter yellow and solid color (no other color highlights). Canary blennies also have a poisonous bite, though I don't think they're very dangerous to aquarium owners. Just something to consider if you have kids. Probably no more dangerous than a bee sting.
Midas blennies can be bright orange/yellow with blue highlights on the eyes and a black spot in front of the anal fin. However, they can be much darker/duller. I got one online that was grey with barely any yellow. I think their color depends on where they're collected from. It's rumored that midas blennies mimic the color and behavior of female lyretail anthias. While most blennies stick to the rock work and don't swim around much, the midas blenny behaves more like an anthias, swimming in open water and eating free floating food rather than food on the rocks.
I've had a midas blenny for several months now. He's pretty cool, great color. He likes to sleep in holes in the rocks, with just his head sticking out. Very cool fish.