Also, Photoshop is one of the programs that supposedly makes this conversion for you. If you edit a document and associate a proper color space with it, it will do all kinds of conversion behind the scene.

The result is that if you choose to fill it with 50% gray, it will absolutely NOT write RGB(127...) into your image.

Stewer mentioned the sRGB color space. If you actually tell Photoshop that's what you're working in, and that your monitor is in that space, and that you intend to print in linear space, then when you select 50% for a fill, you're actually filling it with 73% white.

Most tell photoshop "don't touch my values - just do what I tell you", so you get what you choose, and it previews exactly the same in other apps.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)