Welcome to howtoairbrush.com
"iv been airbrushnigfor about 1 week but im trying to do the $100 effect"
Most of your questions will be answered by taking the time to go thru and learn the basic so they become 2nd nature. Without that strong foundation $100 effects will be something you chase without accomplishing for a very long time. Sorry there are no short cuts, putting the time into learning, practicing the fundamentals and getting them down cold is the only road to success. You need to walk before you can run. No one was born an airbrush artist, kustom painter to be good everyone put the time in to learn dots, lines and most importantly killer shading skills. If you got that all down in a week you set a worlds record............................
Its great to stretch out and try new things all I'm saying is don't forget to get the basic's down....
Spray yellow over black what do you get?? If you applied enough yellow paint to turn a black shirt yellow it weight 20 pounds :-), not good.
By the very nature of spraying paint thru an airbrush the color is transparent the yellow needs a light gray, white to bounce off of on a black surface. You apply white let it dry and apply your yellow. The less paint you use the better.
check this tutorial out
How To Airbrush - Airbrush On Black Surfaces step by step article
hope that helps