As for the feet, when you are applying multiple alphas to your avatar, you will have to "add" them rather than just "wear". When you "wear" a new alpha layer, it will detach all of the others to apply itself.
To "add" this alpha, simply right click on the alpha layer that you want to add, and select "add".
For your dress, try right clicking on the dress and select "edit" on the pie menu.
When this brings up "build" mode, go to the "textures" tab.
From there, you will see the texture that is applied and you can try to add the new color to the dress by clicking the color box that is right above it. Good luck!