How can I superimpose a graphic over a dark t-shirt?
I want put my site logo over a t-shirt. I've successfully done so with a white t-shirt by following this video tutorial.
With a black shirt, I have a problem with the multiply blend mode. Here is a screenshot for a white t-shirt:
And here is one for a black t-shirt
How can I place a logo over a black t-shirt?
It is exceptionally rare that the same artwork is appropriate for both light and dark printing. In 99% of cases you need to change the artwork to work on a dark background if it was designed for a light background.
Most companies delivering logos will deliver a "reversed" logo version for just this purpose.
Obviously you are not using the YouTube logo for your shirts. Without seeing the are you are using there's no telling what your specific issue may be.
The short, general, answer is.... reverse the artwork if placing it on a black background.