It is actually exceptionally hard to get an exact match between the VFD and the white LEDs. You are better off trying to match the raw color of the lens so that everything looks uniform when "off". A bit of planned contrast when the unit is powered is (in my opinion) more desirable than something that _almost_ matches, but not quite.
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Paul Grzelak
200GB with 48MB RAM, Illuminated Buttons and Digital Outputs