Which color packs overlap?

I have purchased 2 packs with the coins I have earned, so I can understand what you mean as I have 2 yellow colors overlapping. There are many colors within the packages shown below that you can barely notice any tint difference in play.

It is completely up to you in the end which packages you would like and which tints or variations you would like to enjoy the game to its fullest, but my recommendation would be: Holiday package and the Mardi Gras package. Both packages + the original set give you the main set of colors required to illustrate a proper, defined picture.

My reasoning:

Between the Mardi Gras package + the holiday package + original set you gain:

• Red[removes red scale package, half of fall package, part of neon package]
• Purple [removes spring and neon package]
• (2 different tints of) blue[removes bluescale package, part of spring package, beach package]
• Green [ neon package ]
• Yellow [removes fall package (see brown below), part of spring package]
• brown [removes fall package, ice cream package]
• Different shades of black - gray[removes grayscale package].

The reasoning above accesses every package (besides minor differences in the shade packages).

Sidenote: I wouldn't bother with the shade packages at all.

Take a look at the screens I have provided below.