I need to make a spiderman cake with whipped cream icing. I do not have much experience with Whipped cream icing. Can I get dark colors with this icing? Do the colors bleed? Is there a recipe that is best for decorating, that holds up the design really well?

whipped cream icing may not hold its look very well..
I've never used whipped cream icing.. but if its the taste your looking for..
I would use buttercream with milk - in my own opinion - I think when I add milk to my buttercream it tastes more rich and whippier lol
And will hold it's design and not melt.

I know my grams made a cute bootie cake with whipping cream.. it looked good, but maybe a melted look... I don't know if it will work well if your live in a place with a lot of humidity.

I decorate with whipped cream icing a lot (most of my cakes are WC) It is very difficult to achieve a saturated color. I usually stick to lighter colors, and decorate with chocolate decorations (which don't break down on the cream like fondant would.) Also, sometimes I will use the WC icing to ice the cake, and then decorate w/buttercream in the darker colors. Just beware - the longer the cake sits (in the fridge, of course!) the more likely the colors from the BC will bleed onto the WC.
I can tell you - you CAN pipe with WC! I have done borders, dots, scrolls, even basketweave. Try to add a gelatin to stiffen it up a little, too! And make sure your bowl, whip and cream are SUPER cold before whipping to STIFF peaks!
HTH!

Whipped cream frosting or Bettercreme doesn't achieve dark colors well. I usually tell my customers that they will have to use buttercream if they choose dark colors. Or if the main color of the cake is light in color but the border is dark then I can do whipped with a buttercream border.