Simba's Pride, like all sequels other then Fantasia 2000, aren't apart of the Disney animated canon. So is it canon?
Some fans don't consider it canon due to the inconsistencies.
For example the color problems and design changes between the two films. I've always attributed both of them to the characters aging. I've always found it obvious that they've aged, and coloring can change with time (even eye color).
The design mistakes between the film are most likely due to the fact it's a direct-to-VHS sequel. Disney movies don't tend to get top animation unless they're in theaters. It makes sense too. Why spend so much money and time on a direct-to-VHS movie?