From my experience: User comes at the bottom of a long form, tries to click the button to go further and it doesn't work. No idea why it doesn't work, it just doesn't. Then has to go on a wild goose chase to find why somewhere in the form something isn't validated; nothing of this is highlighted so good luck finding it.
And greying out/making this transparent in no way comes anywhere near a decent contrast rate for people with non-perfect eye-sight.
From my experience: User comes at the bottom of a long form, tries to click the button to go further and it doesn't work. No idea why it doesn't work, it just doesn't. Then has to go on a wild goose chase to find why somewhere in the form something isn't validated; nothing of this is highlighted so good luck finding it.
And greying out/making this transparent in no way comes anywhere near a decent contrast rate for people with non-perfect eye-sight.