Increase in 20kg increments?
I was thinking 25!
Well...
The colour makes a difference to me.
If you start with a green either side...
You then add the 1.25kg (iron) and 2.5kg (iron) as incremental.
There is a black 5kg Bumper plate.
Anyway...
Once you progress past the green one, the next one on is yellow. Once u finish on yellow (with the 1.25 2.5 and 5s) then ur up to blue then up to red.
Once you got a red on + 1.25, then red + 2.5, or whatver.. the next one is leave the red on add a green, then leave red on add a yellow, then leave red on add a blue, now ur up to 2 reds either side. And repeat, red with green, red with yellow etc.
You dont even have to be able to count it. The colours just work out that way mathematically for you.
IF there all black, then it all gets confusing.
So easier to have 1.25, 2.5, 5, 10 (10+5 you already got = 15), then 20, (20+5 you already got = 25).
Makes sense to me!