You're focusing heavily on the word "accuracy", but you're discussing the topic of skills. In an educational setting, the word "proficiency" better represents the goals of teaching, and teachers often measure proficiency by reporting the students' accuracy on tests. I would try to use the more appropriate word, as it will help reduce confusion.
Also, progress is an appropriate metaphor when teaching. An accuracy test is a single-point-in-time measurement, but progress is measurements over time. Even when you're reporting on the scores for a single test, it's part of the overall journey towards mastery.
As far as a confusing display, I agree. The colored circles are static and do not indicate anything. Your groupings aren't really ordered or complete.
Consider a display like this:
1 digit Needs improvement | Mastered
multiplication 0% 25% 50% |75% 100%
Tables of 1 90% [ | X ]
Tables of 2 80% [ | X ]
Tables of 3 85% [ | X ]
Tables of 4 92% [ | X ]
Tables of 5 0% [X | ]
Tables of 6 30% [ X | ]
Tables of 7 50% [ X | ]
Tables of 8 0% [X | ]
Tables of 9 0% [X | ]
You could still use colors to highlight the skills that need improvement. But this solves some of your problems of ordering, grouping, while still indicating whether or not the students have achieved mastery.