The following can be tagged on to other systems to help with compression of numerical data.

0 - black
1 - white
2 - red
3 - orange
4 - yellow
5 - green
6 - blue
7 - purple
8 - pink
9 - brown

So if you were using the dominic system to memorize a string of numbers such as

225 (assuming 22 is Bugs Bunny(tm) chewing a carrot)

you could have Bugs Bunny chewing a green carrot.

If it was 522 it would be a green Bugs Bunny(tm) chewing a carrot.

5225 is 4 digits no need to mess with it.

or even mix and match things like

(22 as above, and 07 as James Bond sipping a martini)

Bugs bunny sipping a martini while bathed in red light.

2222222222 could become a completely green picture of bugs bunny chewing a carrot (5 sets of 22) to help compress the data therefore chunking for longer term storage. . .

It's also good for the number rhyme system nine twos in a row could be a brown shoe.