Blue means respond in the arrow's direction and red means the opposite, which teaches controlling an action by a rule and suppressing an unwanted impulse.
Yes, on MentalMath this game is free and requires no registration.
At that moment the child suppresses the natural impulse and adapts to the rule, training attention and self-control together.
A child who can tell colors and directions apart can play from about age 7.
Yes, it works on phone, tablet and computer; 5 minutes a day improves how fast the child adapts to the rule.