I think I remember a video of Mark or Grant (found it here) doing a repair like this: light blue frame that gets chips filled with blobs of red nail polish. This is a "visible mending" repair which is awesome and becoming a style of sorts (more for clothing, see the last paragraph below).
The only larger paint resource for Rivendells seems to be here:
http://www.cyclofiend.com/rbw/color.html (referenced by Rivbike here:
https://www.rivbike.com/pages/frame-colors-frame-colors)
And it does not have a particular color for Appaloosa's.
That said, I have tried color matching on a few bikes by rolling it into a hobby shop and picking 2 or 3 testors colors then mixing and matching knowing that it won't quite be right. Always looks great from 6' away, easy to notice from 1' away. Worked GREAT on a Cheviot (orange) and just okay on a Hillborne (gray-blue).
If you do your own paint repair with nail polish or testors paint, then I strongly recommend:
(1) fill the chip with thin layers of paint until it is just proud of the surface of the original paint. In other words, make that little paint blog that is too tall.
(2) Reduce it to level with the original paint using some mineral oil on a cloth that doesn't lose any threads - I use a credit card to give the cloth some consistent pressure to keep the paint smooth. This is more art than science. If you go completely wrong then just use a little more mineral oil to remove all the fresh paint and start over.
This is better described by a company that sells what appears to be very expensive mineral oil:
"
Visible mending" repairs are awesome:
https://www.nytimes.com/2020/03/12/style/visible-mending.html. From that article: "Showing off your patches, visible menders say, draws attention to the way a garment’s life span has been extended. It also subverts the notion, long held, that mended clothes are worn by the poor, while the height of luxury is buying a new wardrobe every season. 'We’re saying the opposite with our mended clothes,' Ms. Sekules said. 'The pride in the look of a mended thing, that’s pretty recent. That’s now.' "
Visible repairs show off that you use your bike while maybe acting as a minor theft deterrent, all good stuff.
Stickers over chips also work nicely.
Take care,
Abe