You don't even have to decode the actual number, just comparatively figure out which one 'looks bigger'. In more steps than necessary to be abundantly explicit:
Step 1: group into two characters each.
Step 2: know that hex is an extension of decimal that adds the digits A-F after 9. So just like 0<1, 9<A and A<B etc.
Step 3: find the biggest and smallest groups by comparing the first digits of each. If they match they're pretty close.
Step 3a (optional): guestimate the intensity of each color by thinking of the first digit on the scale from 0 is least intense to F is most intense. (5: somewhat less than half, D: pretty close to max, 1: almost none etc)
Step 4: use your knowledge of additive color mixing to guestimate the color.
You don't need to be able to map each digit to its' decimal equivalent first to get a general guess. If you're missing Step 4, then you can still figure out mostly-primary colors like #D53A1F. Step 1 should be trivial. Step 3 can be guestimated.
Step 1: group into two characters each.
Step 2: know that hex is an extension of decimal that adds the digits A-F after 9. So just like 0<1, 9<A and A<B etc.
Step 3: find the biggest and smallest groups by comparing the first digits of each. If they match they're pretty close.
Step 3a (optional): guestimate the intensity of each color by thinking of the first digit on the scale from 0 is least intense to F is most intense. (5: somewhat less than half, D: pretty close to max, 1: almost none etc)
Step 4: use your knowledge of additive color mixing to guestimate the color.
You don't need to be able to map each digit to its' decimal equivalent first to get a general guess. If you're missing Step 4, then you can still figure out mostly-primary colors like #D53A1F. Step 1 should be trivial. Step 3 can be guestimated.