To set a color for a Project, open the Project, go to the eye icon and select 'Force Colour'. Then select a color for the Project.
To remove the colour, go back to the 'Force Colour' option and once you get the window for selecting a color press 'Cancel'. When asked if you want to 'Remove Force Colour'. Hit 'Yes'.
To see the Project Color in the Hourline and Long Form the corresponding settings have to turned on in Toolbox > Settings > Hourline/Objects Tree/Personnel Tree > Use Project / Client Colours.
The Project Colour can also be applied to the Web User Access Tiers, so bookings related to a project that has a 'Force Colour' will appear in the Web/iOS/Mobile Web Client with that specific colour.