Widget colours

[Colli Wobblers]

Hi I am using the dark start theme but my clock backgrounds are now too dark now I was wondering how can I create a custom theme of my own and play around with background colours in text boxes etc. nothing too complex just a few subtle changes.

[Colli Wobblers]

In fact if I could just change text back ground colour in my link boxes or if there was a few colour alternatives to just dark widgets maybe a spectrum box for example.