I think that we're all making out the silver/white tyre problem to be more of an issue than it really is.
For a start, as said before, it's planned that the silver tyres will never be used with the white tyres in the same race. So that means that - ignoring the intermediate and wet tyres - the only colours visible at a race will be silver and yellow, or white and red.
It can be assumed that the coloured tyre is the softer compound, and that the 'white' tyre is the harder compound (as silver looks similar to white). However, silver is slightly darker than white, so it will be easier to tell apart from yellow, whilst still looking 'white'.