Not much, many JM's bronze out in the summer. You could always paint it ;)

*edit* that's a joke, don't paint your tree

Kind of depends on which cultivar it is and how much sun it receives. And where you are located. Some red leaved JM's bronze out in too much shade - others do so in a lot of hot sun. And a select few hold their color very well regardless.

I've herd the term Blood Good. Is that a specific Verity?

Yes, 'Bloodgood' is a very well known older and popular cultivar of Japanese maple but it is a larger growing upright form with wide, purple-red leaves, not a weeping dissectum. It does have a tendency to bronze out (turn a reddish green) in full sun in hotter climates. 'Emperor I' is very similar but holds its color better.

A lot of the reds, upright or weeping, turn green or red-green mid-summer. Sometimes it's just how that cultivar behaves, sometimes it needs more sun to stay red. It's not always a bad thing, though-- often the ones that have turned green will push out new red growth, and that looks pretty.

Is your tree planted in shade or part-shade? What zone are you located in?