[ENH] Scatter Plot Graph: max discrete values colors and shape

[jerneju]

Issue

Fixes #2782

Description of changes

Includes

• Code changes
• Tests
• Documentation

[codecov-io]

Codecov Report

Merging #2804 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #2804      +/-   ##
==========================================
+ Coverage    76.2%   76.21%   +0.01%     
==========================================
  Files         337      337              
  Lines       59665    59697      +32     
==========================================
+ Hits        45470    45501      +31     
- Misses      14195    14196       +1

[lanzagar]

• I have a much worse color pallete (gradient from red to blue with many similar colors).
• Triangle appears twice in shapes
• "Other" marker does not have the right color in the picture (different from legend)
• Maybe for next PR : picture and legend should have the exact same colors/symbols

[jerneju]

I have a much worse color palette (gradient from red to blue with many similar colors).

Color palette is variable dependent. See variable.py.

[lanzagar]

Color palette is variable dependent. See variable.py.

Which means your changes here are problematic because they do not handle this...
The colors are determined based on the variable (number of values), but you change the values before plotting. So you can't use the palette for a variable with e.g. 100 values after merging that into 11 values.