Some mortars can be more tricky than others, as a lot depends on the texture and absorption and composition of the particular mortar used, so it is important to try samples sachets first. You will then be able to carry out a pressure wash test after 24 hours. If the colour remains fixed, then you could expect many years of durability.
Newer mortars will still be curing, this means that higher levels of lime can be at the surface. This needs to be taken into consideration, even if it is a cement based mortar and no lime was added, lime can still be created from the reaction of CO₂ in the air with the calcium hydroxide within the cement. This causes 'lime bloom' which can affect the durability when applying colour corrective remedies to those areas.
Mortar tinting should be carried out in the warmer drier months.