src/vs/platform/theme/common/colorRegistry.ts/ifDefinedThenElse
export function ifDefinedThenElse(ifArg: ColorIdentifier, thenArg: ColorValue, elseArg: ColorValue): ColorTransform {
	return { op: ColorTransformType.IfDefinedThenElse, if: ifArg, then: thenArg, else: elseArg };
}