if it has 6 power tubes its a coliseum, if only 4 then its not. the coliseum heads were designed to be much more powerful. the stripe is located on the back of the amp, above the power cord. there either will be none, a black dot or stripe, a purple stripe, a red stripe, a blue stripe, or a green. the no-stripe represents the initial offering of the mark III, and each stripe from there represents refinements and changes made in the amp. basically the no stripe sounds distinctively like a mark III, the green is pretty close to the IV that replaced it, and somewhere in the middle (red/blue depending, there are different opinions on that matter) it sounds similiar, though not the same as, a IIC+. I listed the stripes in order, and later stripes tend to fetch a higher resale value than earlier, though there aren't many no stripe III's, so those sell a little higher also