The colours used in the main body of the receipts area can be changed from the default colours
The Merchant Facility tab can be found within the Payments2Us menu (Top right picklist in Salesforce - Select Payments2Us), or it can be found under the "More" at the end of the tabs. (In Salesforce Classic - It can be under the "+" at the end of the tabs)
Once you have clicked on the Merchant Facility Tab, select the appropriate List view (Example - "All Merchant Facilities") and click into Merchant Facility you wish to update.
2. Scroll down to the Receipting section
Classic - Receipting heading
Lightning - Receipting Format PDF attachment
3. Select the colour based on HTML colour codes
Colours can be chosen using this chart