Simply, that is not a continuum.!
This is NOT a continuum
This IS a continuum
Your example is precisely NOT a continuum.
What's the best word for the item you present? Probably just a "chart" or "color pie chart".
Words like "stepwise", "discrete", "blocky" come to mind.
Secondly, regarding your question "circular -- one end meets the other"
Here's "one end does NOT meet the other" -
and here's what you describe -
The end result here is:
(1) you are completely wrong to refer to your example as a continuum, it is a "stepwise" diagram. I'd call it a "chart" or perhaps "legend" or "key".
(2) regarding your question on the "ends meeting". there's no particular word for that. Sure, you can say something is "circular" in an expressive sense, even if it is not literally a circle. (For example, we say "circular logic".)
(Note) there are technical terms, such as, "venn diagram" "bar chart" "Gantt chart" for certain types of diagram. These may help you. There's really no especial term to distinguish "stepwise/discrete" from "smooth/continuous". You'd just use those four words in context.