So manic panic hair colors are great and better for your hair, but your right that they fade quicker because they're semi-permanent. You want to use a gentle acid-balanced. shampoo and conditioner, especially a shampoo that doesn't have a lot of soap in it. Your stylist can probably recommend products, but I have been using I recommend Camomile Luxurious Volumizing Shampoo and conditioner from Aubrey Organics. It's about $10 for each and you buy it at Whole foods, some Health Food Stores, or online. It smells great and really does add volume to your hair

http://www.aubrey-organics.com/ProductInfo/009.aspx

http://www.aubrey-organics.com/ProductInfo/018.aspx

You also might try a protein conditioner once a month or so. I use Aubrey Organics Blue Green Algae Hair Rescue Conditioning Mask

http://www.aubrey-organics.com/ProductInfo/801.aspx

But there are other masks that are good too like CHI Keratin Mist or Redken Extreme CAT Protein Treatment.

I know you don't want the color to fade too fast, but I think you should shampoo and condition at least twice a week. It'll make your hair look better and won't fade much faster if you use good stuff.