I started with colour this way. I 'rebought a filter set last year to remind me how it all used to be. Yes, the old unicolour matrix I have looks to be faded, but gets you going in the right direction.
Kodak and beselar (I think) made similar things
A small calculator to figure the new exposure time when swapping out filters was the best tool, yet biggest pains with discrete filters. The Kodak print viewing filters had a cardborad insert that has the filter factors of 05 to 50 of each colour printed on it.
As other posts have noted, the print viewing filters are a very powerful tool when you are starting to learn how to print colour. A printed ring around is close to as useful, but Ai still likelt the viewing filters more.