The problem indeed seems to be limited to the Mac platform and senior LV developer Greg McKaskle posted the following explaination on info-labview:
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The mac version of the rendering engine fails to allocate rendering context larger than 512 pixels wide or tall. When your meter gets above about 710, that is when the radial ramp goes above 512 and the allocation fails. When it fails, LV reverts to using a noninterpolated ramp.
Future versions of the render engine will hopefully not have this limitation or we will learn to work around it.
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happy wireworks
Urs