I am at the bottom of the curve here. I have a natural gray blank that I used a gunmetal base thread with a slver metallic inlay. Looked great. I have always used color preserver but decided not to on this rod as the silver was a little lost in the gunmetal. As expected the gunmetal darkened up nicely and the silver stepped out. Problem is the two tag ends of the silver show through as a rusty gold under the gunmetal. I can't see anyway to avoid this. Would a black thread have been better as the gunmetal is almost black now. If that is the case then it seems that black would be the only color thread you can use if doing an inlay.

Threads used without color preserver tend to go transparent and take on the look of the blank underneath. Black may be the only color that doesn't. It just stays black.

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If you keep your inlay extensions really, really short, say about 2 wind overs, they are not that noticeable even on those transparent threads. Be consistent, and start and stop them at the same point and make the starting and stopping point of all inlays along the same axis.

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Another alternative is to do a 2-3 wind trim band. I know it is not the same effect, but if you use the wrap around blank and fingers then pull through method you will have no tag ends to show. Just an option
Elrod