These animations (for both line/fill colors) define numeric tag/expression whose value is compared with a value/paint table to find which is the paint to be used.

At runtime, for a value x of the code, the paint will be chosen so x will be between the paint value and the next paint value.
In details, the rules used to choose the are:

• The value/paint table is always sorted from lower to higher values.
• The value/paint table is scanned from the top (lowest value) to the bottom (highest value).
• During the scan a paint is chosen if its value is <= of x and the next value in the table is > of x (or there are no more table rows).
• If x is < of the first value of the table (the smallest), than no paint will be used (transparent object line/fill).