You can either google hex code for the colour Black or Blue or if there is a specific colour you had in mind you can download a chrome extension called ColorZilla which allows you to select a colour on a website or image and it will give you the hex code.
Go to Settings > Branding > Preview in new tab > you should see it in your browser URL. It should look like this https://tracking.tryhutch.co.uk/my-store but instead of my-store it would be your brand name.