This is a look back from the later quaestion, for some search only shows this post instead of that one.
You can mark the accents in a colour different than the base letters, without the text-shadowing hack (demonstrated in other answers) in this way:
ñ to n͏̃) where the combining grapheme joiner (U+034F) is required after the base letter and before the combining diacritic marks.There is another workaround not as evil as text-shadowing, but will introduce some offsets. More on that down below.
This is 10 years after the quaestion was posed, but allow me to answer it.
I stepped into this problem on my journey through learning Sanskrit, as the Indic scripts mark the vowel on top. The fonts work same as Latin ones, with ते drawn as त and a े above.
Then there was the fiddle in the aforementioned post, of which the expected behaviour is with red diacritics and blue base letters as shown in the image. Happy after some tests, I decided to make a colourful grammar chart, and shared it with my mates. Later on I get complaints that no one other than me is able to open the correctly rendered chart.
Turns out that Chromium doesn't support this for some how. I tested the said fiddle on both my Win10 and Win11, for Chrome 131.0.6778.109, Edge 114.0.1823.86, Brave 1.73.97, Chromium 131.0.6778.108 and Opera 115.0.5322.77. All shown just blue. Only Firefox works.
As this other answer from the mentioned related post suggests, there is a workaround using another typeface/weight. The visual effect is worse than shadowing though.
