Improve color contrast accessibility

[neonpixii]

in order to make the app more accessible, along with improving the font weight (#15) and adding a font better optimized for readibility (#17), the color contrast of the themes could use some work in some places.

the Default theme is especially inaccessible, with the pale blue keys and the red non-pu keys being almost completely unreadable and the green ones being just slightlydifficult to read.

the Light theme has quite good contrast overall. the Dark theme's contrast is a bit on the low side, but i understand a lot of people like low contrast dark themes look, so i might reccomend adding a second dark theme that uses high contrast colors.

these changes (along with a much-needed increase in the font weight) would go a long way towards improving useability & accessibility of the app.

thanks!

[timeopochin]

Colours are hard! I’m planning to take some time to refine themes, and I think I may implement a section of the settings to set custom colours.

Thanks for the suggestion