I did my overlay as white text on a black background. Then took the file (I saved to .pdf) to a local Kinkos. They were able to print it for me onto a semi-gloss self-adhesive vinyl ($.50 for a single sheet).
It turned out pretty nice but, as said above, the white was too white vs. the other gauges. That said I suspect the only person who would ever notice is me (is that close). But of course, outside this forum, the only person who ever notices any deal on my car is... well... me.
I bet the extra white will look OK on the speedometer alone - it may look like it was intended (the speedo will look a bit brighter than the other gauges).
Also note that the only text on the gauges for which those two fonts is NOT appropriate is the "MILES" on top of the speedo. However, if I recall correctly you can't see that behind the bezel (I am thinking it was there for assembly/sorting - as in "this is a MPH speedo" whereas there may also have been a "KILOMETRES" label?)