How to make color adjustment

[Su Myat]

Hi all,

how can I make the veins more obvious.

[c.pfaffenbichler]

Could you please post a screenshot with the pertinent Panels (Toolbar, Layers, Channels, Options Bar, …) visible? 

Sorry, my mistake. 

Edit: 

[MarekMularczyk]

or you could bump up the contrast with Brightness/Contrast adjustment or Levels adjustment.

[didiermazier]

You could try Image > operation > working on chanels