Form validation state colors aren't colorblind-friendly

Created by: JackDanger

Changing these values for v3 isn't going to happen—it's quite a stark change for folks who simply want to upgrade to the latest. v4's colors can and will be changing though, so we can revisit then.

Issue #14744 (closed) was closed a year and a half ago to postpone an accessibility issue until v4. Due to the ongoing problem I propose reopening it and attempting to create colors that don't ruin the experience for the 96% of people with color vision but allow the 4% without to still use bootstrap-constructed forms.