You can change the color of each bed individually by selecting the bed when the bed menu is active and picking or entering (use Hex Color Codes) a color in the right hand menu.

But you can also set a default bed color for the plot. This lets you set the default color for any new bed you add to your plan. There is also an option to apply that default bed color to all beds on the plan if you wish.

To set the default bed color for a plan, simply open the plan or plot settings menu. This is in the right hand panel (hit the cog in the right hand menu to open the plot settings panel)

Picking a default bed color in plot settings menu

Click on the default bed color field in the plot settings panel

Select a suitable bed color or enter a color hex code (to set an exact color of your choosing) and hit Update

If you wish to change all beds to the selected color, hit the [Revert all beds to this color] link