My favourite colours to use for boys' cards would be blue, grey, red and green. Or in Stampin' Up! talk as pictured below, Pacific point, Going Gray, Real Red & Wild Wasabi.
The greetings "Wish Big" and "Best Wishes" are from the Short & Sweet Stampin' Up! stamp set. The Patterned Designer Series Paper is brilliant if you're going for a single colour card look.
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