sideoftheroad Might I suggest that since most P-40s use inverted engines and that combined with plastic spinners very often end up with those nasty black rings Perhaps its time to step up to an aluminum spinner. If you must use plastic then definitely the color to use is black as this tends to hide the rings.
TLH's link above shows some aluminum types (I also would avoid the carbon fibre types) and here is a link to the Dave Brown Vortech spinners:
https://www.dbproducts.com/store/
John