The colour of your logo can be altered to show either the original colour of your logo or black/white - dependent on whether you have a light or dark coloured background.
To manually change this, hover over 'account' in the top right corner and select 'settings', select 'design lab' from the left hand menu and open the logo tab. Under your logo you will see 'logo options'. Once you have your design set and colours picked, toggle between the automatic and coloured buttons for each template to choose which you would prefer to use, coloured being your full colour logo, automatic being black/white.