yes, all print work should be submitted in CMYK format, that's the format they print from, all it does when they take rgb to cmyk color is it puts it in 4 color format instead of 3 color format so it could throw your color off a little bit, but very minimal, so what people typically do is convert to cmyk and adjust if needed, sometimes you want ya colors a little more saturated or whatever and cmyk can at times change the saturation of color a bit but that's about it, I've never seen even a shitty printer make it look but so bad, usually bad colors come from one of the ink barrels running low. as long as all ink is full and it's set correctly your str8. it will look just like it, also they could have a fucked up printer? but that's cause for a refund anyway