If you really like the blue ones, just get them. If you are concerned with legality, just buy amber bulbs. I'm sure that once your signals are on, they'll emit an amber color and the blue lens won't have any significant effect on it.

And if you don't like the way they look amber when the light isn't on, invest in a set of Sylvania Silvervision bulbs. They looks silver when the bulbs aren't on, and light up amber.