So this rectangle area is computed from several data points over the sample interval and displayed as one rectangle.
We take in the initial value at the start of the interval, the closing value at the end of the interval, the high value during the interval and the low value during the interval.
So let’s say on a given 5 minute interval Open 5/ Close 3 / Low 1 / High 12,
Since if Open>Close=Blue if it had been the opposite (Open<Close) it would have been Yellow.