Rainbow Ore introduces the aptly named "rainbow ore".

Running both mods results in this:

Failed to load mods: Error while loading recipe prototype "unstable-rainbow-ore" (recipe): Key "icon" not found in property tree at ROOT.recipe.unstable-rainbow-ore.icons[1]

The resource rainbow-ore only defines the icons property and not the icon property. I don't know if there's an elegant way to grab the merged icon, but pulling icons[1].icon if icons is defined would at least let this work (it's a single-record array in this case).

EDIT: Accidental post.

Yeah, that one's on me. I'm just reading "icon" without consideration for icons. Not really sure why. Should be simple enough set to set the icon to "resource.icon or resource.icons[1]". I'll have to run some tests to make sure it's working correctly in the morning. Might be a good time to implement some additional functionality, as well - like an include list and maybe some planetary restrictions for ore generation. I'll probably get an update out tomorrow.

Fixed in 1.1.4. Also added an option to restrict some ores to their respective planets - currently Tungsten and Calcite to Vulcanus. Make sure to toggle this off if you don't like the change, as it's on by default.