3551 and 3651 are calendared and not high performance vinyl.
I'm not sure that the texture of the vinyl has a whole lot to do with what colors you can hit. My guess is your over saturating the vinyl with ink. If you have an orange peel/mottled look to your darker solid colors and your darker colors bleed into each other, your either putting down too much ink, not running enough passes, temps are too low, or all of the above.