Every main GUI (not including experimental UIs) has been updates to either closely resemble the High Contrast resource Pack
Doesn't affect any blocks or items
Still a work in progress, do plan to make it available for earlier versions
Go into Minecraft, go to Options > Resource Packs > Open Pack Folder. Move the file into your "resourcepacks" file. Go back to Minecraft, find the resource pack labeled "Better High Contrast", and click the arrow to make it active. Click Done in Minecraft and enjoy!