I want to render magenta colored (#E40045) type on a dark blue (#303C49) background.
Preview in AE looks sharp and crisp as in the screenshot below:
After rendering as Quicktime Apple ProRes422 this is what the edges of the type look like:
Tried several codecs, nothing worked except lossless animation…
Nothing wrong. Simply an unfavorable combination. Many compression algorithms reduce the available color range and dark blue-ish tones vs. glow-y magenta tend to be on opposite ends of the spectrum in YUV and simialr color models. Combined with chroma undersampling such as used by ProRes 422 it simply means that colors deviate and in the areas, where two colors meet, but only every second pixels chroma is sampled and the rest interpolated you will get soft edges. It's fundamental computer stuff that you cannot avoid. Even if you may not see it in uncompressed intermediates, it will come back latest for final encoding in e.g. H.264. So rather than trying to solve these issues on the wrong end, re-design your artwork to minimize those issues like avoiding perpendicular straight edges or at least introducing those soft areas via controlled methods by using sub-pixel placment and thus getting proper antialiasing.