Oh, well, when I say "expand," I just mean that, out of 16 possible colors, only 8 are used in CSet 8 (assuming you're using default classic tileset, as your screenshot would suggest). If you open the tile page and edit a tile, you'll see the 4x4 palette color grid on the bottom right, and when you're on CSet 8, the 3rd row will be empty (as will the 4th, except for a stray blue). So if you need more shades of red, you can put them there.
I only suggested CSet 8 because it has a red focus. When I was adding more shades of blue for something else I was doing, I put them in CSet 7 because that has a blue focus. But you can add them to any non-2/3/4/9 CSet and they'll stay consistent no matter what dmap palette you use. 8-bit just allows you to use multiple CSets at once, but if you can put all the colors you need in a single non-2/3/4/9 CSet, you won't need 8-bit, then you can place it in any level and it will look the same.