Colour should be used to highlight the important information. How do you decide the URL is more important than the dependencies for -Si? Why is the number of packages being installed highlighted yellow when that is only used for warnings?
Agreed in general, but it makes sense to reuse the same colors for the same classes of information across different commands. The package names, repositories, groups and versions have color in -Ss/-Qs so it makes sense to reuse those same colors in the -Si output and perhaps elsewhere like the -Su output. It makes it easier to visually jump to the right place in the output if there are some consistently colored lines. It doesn't all need color. I don't use Pacman enough that I'd benefit from any of this though... only upgrades, occasionally package installation and rarely a search or query command.