I like the colors. I think both GMK Birch and this set pull these sorts of colors off nicely.
I think your base kit is a bit bloated. Seeing as you're using three custom colors, I think you'd do good to cut some of the less commonly used keys (e.g. 2u Shift) or move them into a separate kit (e.g. accent spaces + small spacekeys).
Edit: One more thing, you don't need R1 1u `~ and R2 1.5u \| in the alt alphas kit since they're already included in base. What you should instead add are cyan R1 1u \|, R3 1u \|, R4 1u <>, alt homing F and J, as well as cyan 6.25u and 7u spacebars. Basically, any alpha-colored keys in base that don't already have a mod-colored counterpart should also be represented in the alt alphas kit.
Adding a second Tab to that kit would also be a good idea. This allows users to cover two full boards if they buy base + alphas (assuming they use two slightly different layouts).