Cake Decorating

My 8 yr old son wants a spongebob cake for his birthday and I couldnt get it from any bakery shop in my area...so I took matters in my hands and decided I will make it for him.

Since I am a amateur at cake decorating I am turning for help from you.

I started by baking a Betty Crocker french vanilla cake, and when its ready its tasting tooo sweet, thou I made it by follwing the directions on box.

I was planning to mix blue color with Betty Crocker cake icing or cupcake icing to make blue base for my cake and then use some orange color same way to make my pineapple house.

Now I am really worries is it a good idea or will it sweeten the cake further or is it going to work.

Plz Plz help me....