Prepare 2 cans of gum paste. Roll out 1/8 in. thick; cut 16 squares, 3 x 3 in. Let dry overnight on cornstarch-dusted boards. The next day, turn squares over and let dry completely overnight. When dry, attach squares side-to-side with thinned fondant adhesive to form blocks; let dry.
Add trims. Tint 24 oz. of fondant blue and 6 oz. each in light rose, green and yellow; reserve remaining white fondant. Using alphabet cutters from 101 Cookie Cutters Set, cut 4 green B, 4 yellow A, 4 rose B and 4 blue Y letters. As needed, cut out centers of letters with craft knife. Attach letters to blocks with damp brush. For borders, cut assorted fondant strips, 1/4 x 3 in. long; attach with damp brush. Let dry.
At reception, completed blocks will be positioned around pillars on 14 in. cake. The 10 in. cake and the bear cake will be placed on top.