Besides the obvious answer that they’re different colours, whether or not you need to use red or blue ink will depend on the type and age of your machine.
All new SMART franking machines are required by Royal Mail to transition from red to blue ink once their last red ink cartridge runs out. If buying or leasing a brand new machine your supplier should only supply you with blue ink.
Older non-SMART franking machines can still use red ink for the time being. Royal Mail is working with the franking industry to eventually switch everyone over to blue ink at some time in the future, but for now red ink can continue to be used on these machines.
If you’re unsure what type of franking machine you own or rent please speak to your maintenance and/or lease company.
For more on franking machine ink click here.Click Here To Compare Franking Machines