The clay in LBC's is naturally a pink colour, so as it weathers the face colour changes. The colour does not go through on these bricks.
If you are changing a few bricks scattered around the wall it's more important to get the colour of the mortar right than the brick.
If you look at most walls the bricks vary a fair bit, but the mortar is the same colour.
When a few bricks have been replaced they really stand out if the mortar is really light. If anything a slightly darker colour of mortar stands out less in the wall.