Yes, this permanent cream color is suitable for both covering new grey regrowth at the roots and refreshing the color on the lengths, as it fits into a regular beauty regimen for these purposes. The key to a seamless result is managing application timing due to the different processing needs of virgin roots versus previously colored hair.
Start by applying the color mixture to the new growth at the roots only, as this area requires the full development time to lift and cover grey hairs effectively. Leave it to process for about two-thirds of the total time stated in the instructions (e.g., if total time is 30 minutes, process roots for 20 minutes). Then, quickly work the remaining mixture through the rest of your hair (the lengths and ends) for the final third of the processing time. This staggered approach helps prevent the previously colored, more porous lengths from absorbing too much pigment and becoming darker or more saturated than the roots. Always follow the specific timings on the product's instruction leaflet, as development times can vary. A final, thorough rinse and application of the included fixing balm will help unify the tone and finish.