Is your feature request related to a problem?

I am colorblind and I am having issues noticing the red background.

Describe the solution you'd like

I would thus like to request 2 new settings to be added :

• A slider for the opacity of the background
• A color picker for the color of the missing items.

Describe alternatives you've considered

No response

Additional context

No response

Ehhhh a color picker is anything but easy to add. https://github.com/tr7zw/ItemSwapper/blob/main/src/main/java/dev/tr7zw/itemswapper/util/RenderHelper.java#L45 this value could be exposed via the config or so, but don't think a color picker for the config screen will happen unless someone has the knowhow and pr's it(also noteworthy that the red-tinted items is actually copied from Minecraft, so might also be something to ask Mojang about). The opacity of the background is the resource pack, not code. You can replace the image with one better fitting your needs(feel free to open a pr).

You maybe could just do a simple button with a preselection of colors and clicking on the button goes through the list of colors. I did not mean a litteral color picker.