Choose one —
• Counter target spell if it's red.
• Destroy target permanent if it's red.
10/4/2004 The decision to counter a spell or destroy a permanent is a decision made on announcement before the target is selected. If the spell is redirected, this mode can’t be changed, so only targets of the selected type are valid.
6/8/2016 Hydroblast can target any spell or permanent, not just a red one. It checks the color of the target only on resolution.