Set different background colour to custom blocks

To set different background colour to your custom blocks, please open your css style file and insert the below strings at the end of the file:

.bl_custom .titleTopLeft {background: #00f;}
.bl_custom .titleTopCenter {background: #00f;}
.bl_custom .titleTopRight {background: #00f;}
.bl_custom .block {background: #00f;}
.bl_custom .usual {background: #00f;}

If you are using a custom block without title, then just change .bl_custom to .bl_simple.