Baral's first ability doesn't affect the colored mana requirements of instant and sorcery spells.

If there are additional costs to cast a spell, such as a kicker cost or a cost imposed by another effect (such as Thalia, Guardian of Thraben's ability, for example), apply those increases before applying cost reductions.

A spell or ability counters a spell only if it specifically contains the word "counter" in its text. If a spell or ability you control causes all the targets of a spell to become illegal, that spell is considered to be countered by the game rules, not by the spell or ability you control, and Baral's ability won't trigger.