You'll want to add some color to your LibGuides! You can change the color of the page tabs along the top, and the boxes in your guide.
To do this, click on the picture icon in the top right of the page and choose "Tab & Box Options" from the drop down menu.
html understands color in a hexidecimal coding system, known as the hex code. Knowing how this system works will help you when you're planning your aesthetics.
The first two digits in the 6 digit code are the amount of red, the next two are green, and the last two are blue. The digits go from 0 to F, with A being the equivalent of 11, B the equivalent of 12, etc. If you really want to understand the hexidecimal system, there is a great explanation on it here: https://www.pluralsight.com/blog/tutorials/understanding-hexadecimal-colors-simple.
For just a quick guide: