Yellowish RF patch is normal. The viewfinder is blue tinted, and so there is color contrast with the yellowish rangefinder patch. When you're in focus the image should be color neutral. The RF patch on the M2 M3 is gold plated.
The latest cameras use a silver rangefinder mirror, and they are color neutral. At least they are neutral on my M5, M4-2, M7.
MP, M7 finder show more contrast overall due to use of coated components in the viewfinder and rangefinder.
The M2 and M3 finders are uncoated. Up to the M6 the finders are uncoated, but still usable nevertheless.
I had a Leica IIIf that had a slightly yellow RF patch, and the stationary image was slightly blue. When you were in focus, the two colors complemented each other, and you had a neutral image.
Leotax S also has a similar yellow / blue combination.
Carena Computer II (made by Petri) from 1974 has a distinct yellow RF patch. There is a slight blue tint in the viewfinder.
On my Contax IIa, the two images are red and green tinted. When the images coincide, the color is neutral. In the case of the Contax, one image is made by silver coating, and the other by gold coating. I'm told that Zeiss stopped doing this due to cost restrictions on the post war Contax cameras, but on my 1955 IIa, it's there.
So, the use of color contrast to distinguish the rangefinder image is a time honored approach used by many manufacturers, including Leica.