HEADER QUALITY IN WP

I have just made a website on WP. When I made the header on Adobe PS it really looks bright but once I uploaded it on WP as a header with the same size which require by the theme and in JPG form. Than the colours of the header becomes very very dull. I have tried it with PNG, GIF, JPG with different resolutions but all the time result is same. I am new to WP as it is my 4day to using it.