mostly i work with irises, tulips and cosmos. that's a lot of colors and plant combinations. having a numbered tag would not give me an easy means of identifying color. permanent markers tend to not be permanent enough (or the color changes). wooden markers degrade quickly (even painted, i tried those) and get lost or moved or stepped upon if stuck in the ground.
having markers that do not degrade in the sunlight, don't easily fall off, can be reused, are not terribly expensive, break or whatever is very nice. this year i finally got a better solution and it helped a great deal come pod harvest time.
what i have found is that a package of plastic beads and ties (little plastic strips with a serated edge on one side that locks if you put it on "right", but if you want to reuse them put them on backwards and pull them on and they can be removed again).
the ties can be bought in packages of quite a few. i have green ones that are about 7 inches long and not too wide so they go through the beads. for indoor use in keeping track of seed container contents i use much smaller ones so they are more flexible and can fit inside small containers. the beads you can find at a hobby store in 1 lb packages of assorted colors.
the coding is the fun part. :)
when i'm working in the tulip patch i mark certain plants by primary color and then secondary color (stripe, flame, edge) and then if i've crossed it i will put those on too with a separator bead of some color i'm not using for anything else at that moment.
i always code the same direction (the first bead on is the starting point from left to right with the knobby end being the left). also if i want to code shape, season, height, etc. those are all available to me as the number of colors available is pretty large.
here is an example if this all seems abstract. i have a late white tulip with red flames, so i can put a red bead on first and then a white bead and then a clear red (late), use a black bead as a separator and then if i've crossed it with a solid purple early tulip i can put a purple bead and then a clear green (early) on. so the final code for this plant is:
red, white, clear red, black, purple, clear green.
if the pod forms and i get seeds then i have both the pod parent info and the pollen source info and don't even have to read the notes to see at a glance what crosses i could be making with other plants if i've left something out.
after i've harvested seed i mark the seed catalog spaces with each code so i know the parents and the cross involved (i also keep written records and pictures).
the coding is really only limited by space on the ties and you can fit around 20 beads on. you can also get different color ties or chain multiple ties together. and then if you want to get really complicated you can do a different code for each type/species/flower bed or whatever suits your fancy.
i was lucky that Ma had a package of metallic tinted colors and mixed in were some clear colors along with the 1 lb package of multicolor from the hobby store. i think i have enough variety for a good long time. if i see a package of different colors at the dollar store i can pick them up and add to the collection... :) i think there are some bright sharp color mixes and some pastels too, but i don't really need them yet.
*cough* so how's them tomatoes? :)
as an aside i also use the ties backwards for holding tender shoots to trellises and then when they've attached the ties can come off and be reused. just be gentle and don't pull them tight and many plants are fine. they can have sharp edges so you might have some marks, but i think climbing plants just work around that sort damage quite easily.