The meaning of a sentence linked by "if only"

It means that using the blue grease paint may accomplish more than one thing, but that at least it will obscure the blushing of the person addressed. There is an implication that it might do more, although this usage ordinarily, in fact, doesn't suggest what else might be accomplished.

if only = even if it's just to . . .

EXAMPLE:

Now might be a good time to explain it to you, if only [there could be other reasons, some better, some maybe worse] to allow you to explain it to your students.