I found that the working parent icon resource was green in arcade and grey in mameui/hbmame. So I copied the arcade resource object across, and now the working icon is green in mameui/hbmame.
I still want to have the red X as an option which will mean an extra choice in the interface options. If you don't choose it you get the red chip, if you do you get the red X.
About the grey chips, there 2 kinds, one with a ? to indicate it hasn't been scanned at all, and the other one has the stop sign to indicate it has been scanned and some roms are missing.