Motivation / Problem

See #8630 for explanation of problem.

Closes #8630.

Description

This darkens the grid lines to one shade lighter than the background, as suggested. It would be easy to go lighter, if desired.

It also changes the x-axis ($0) from black to a lighter grey than the other grid lines, for better readability.

Finally, it changes all greyscale color assignments to use the consistent GREY_SCALE() method.

Profit graph:

Payment rates for vanilla cargos:

Limitations

This does not address the other issues raised by @LC-Zorg. I might tackle the period markings next, but one PR at a time.

Checklist for review

Some things are not automated, and forgotten often. This list is a reminder for the reviewers.

• The bug fix is important enough to be backported? (label: 'backport requested')
• This PR affects the save game format? (label 'savegame upgrade')
• This PR affects the GS/AI API? (label 'needs review: Script API')
  • ai_changelog.hpp, gs_changelog.hpp need updating.
  • The compatibility wrappers (compat_*.nut) need updating.
• This PR affects the NewGRF API? (label 'needs review: NewGRF')
  • newgrf_debug_data.h may need updating.
  • PR must be added to API tracker