Joining a new color with a different gauge yarn?

I started a hat using boucle yarn in the round (size 9 needles) with a stockinette stitch (it makes a cute rolled brim). I’d like to try joining a new color with a less chunky worsted weight yarn in a rib pattern like the hat at http://alison.knitsmiths.us/pattern_beginners_hat.html and then go back and add a couple of boucle yarn stripes. Am I just asking for trouble or can you join 2 colors with different gauges? :shrug:

You could have a couple problems adding a yarn with different gauge. If you continue with the same size needles it could be a very open lacy look, if you used the needle with the correct size for that gauge it would be much tighter in that area… so the hat would pull in at that point. That may happen anyway, too. You might be able to double the yarn and make it work, but I’m not sure.