Paul,
At Lee/Tim's request, I tested an 'Android' beta version of SD - provided at very short notice late on the Wednesday to correct the previously identified 'altitude display issue' - on my flight down to the LAA Rally last Thursday. I reported back to Lee and Tim on the Friday morning that his 'repair' appears to have corrected that fault. During discussion, Tim expressed concern about the readability of the 'Relative Altitude' text on the bearingless target rings - even after increasing the text size, which I was delighted to hear as I still find the 'improved' text difficult to read in an open cockpit. Having considered the options (including your proposal for a white background), Tim decided to further increase the text size for relative altitude on the bearingless rings - giving this 'priority' over the 'Reg' (he initially wanted to 'lose' the 'Reg' completely but accepted my case for retaining it, though with lower priority). IIRC Tim also said he was going to link the relative altitude text to other SD text fonts to make them all simultaneously 'user adjustable' in his next release. He has I understand also 'slimmed down' the thickness of the bearingless rings a bit to reduce the potential to obstruct underlying detail especially when they change to the smaller 'Alert' and 'Danger' sizes.
Following Tim's work with us at the Rally, I now have the latest iOS SD beta which I am still trying to find flight time to test properly. I am however confident that this will resolve the text readability issues.
Regards
Peter