Those status items with color are actually doing it the wrong (old) way. You're supposed to use template images so that the system can apply effects and show it properly in Dark mode. For a template image, the color is ignored. Only the alpha channel matters.
If you really want to defy Apple's recommendation, simply use a non-template image. Don't suffix your image name with "Template" and don't set the template
property in code.
From the AppKit release notes for 10.10:
NSStatusItem appearance and Dark Menu support (Section added since WWDC seed)
There are a number of stylistic changes added and supported by
NSStatusItem, including appearance changes for Dark Menus. Template
images should always be used to ensure correct styling based on the
various states the status item can be in (light menu, dark menu,
inactive light, inactive dark, selected, disabled, etc).
NSStatusBarButton’s appearsDisabled property can be used to give the
image a disabled or “off” look without having the item be functionally
disabled. …