Make new background layers white by default

[CST1229]

Description

This makes newly created background layers white instead of black by default, which fixes a thing i've seen sometimes where people get confused that the sprites they set on their background layers show up as black in-game (since the room editor view doesn't show background layer colors), and is probably more in line with expected behavior.
(And it's also technically a UTMTCE port since it also had this.)

(It seems GameMaker's behavior in this case is still different though. There, that background layers start with color #181818, but get set to white whenever you add a sprite to them.)

Caveats

Notes

[github-actions]

Download the artifacts for this pull request here:

GUI:

• GUI-windows-latest-isBundled-false-isSingleFile-false
• GUI-windows-latest-isBundled-false-isSingleFile-true

CLI:

• CLI-macOS-latest-isBundled-false
• CLI-ubuntu-latest-isBundled-false
• CLI-windows-latest-isBundled-false

[colinator27]

Part of me is a little wary of disrupting existing workflows that do actually want a black non-sprite background... (UT/DR mods in particular would tend to desire that perhaps more than other games.) I wonder if we have any way of doing something similar to what GameMaker does...? Could just be some kind of hack that detects specifically the color black, and then turns white when attaching a sprite (when no sprite was previously attached).

[CST1229]

Could just be some kind of hack that detects specifically the color black, and then turns white when attaching a sprite (when no sprite was previously attached).

GM seems to always overwrite the color if a background layer goes from having no sprite attached to having a sprite attached.