Change plotting docstring to specify integer RGB values

[CoronelBuendia]

Description

Fixes the docstring in _PLOT_PARAMS to specify RGB values as integers in the range [0, 255].

Fixes #3866

Checklist

• I have performed a self-review of my own code
• I have run clang-format (version 18) on any C++ source files (if applicable)
• I have followed the style guidelines for Python source files (if applicable)
• I have made corresponding changes to the documentation (if applicable)
• I have added tests that prove my fix is effective or that my feature works (if applicable)

[paulromano]

Thanks @CoronelBuendia!