Since both of the products you mentioned are relatively inexpensive, the cost to seal the grout should not be the issue here. You could be penny wise and pound foolish by not using a sealer that will offer the greatest longevity. In our opinion, your interests would best be served by using a silicone product to seal the grout. Not only will it last longer, but it is highly impervious to water...more so than lemon oil. Furthermore, we believe that if you elect to go with the lemon oil rather than the silicone, you may find yourself spending a great deal of your spare time sealing and resealing your grout. And, where silicone generally dries to a clear finish, lemon oil tends to yellow the grout.

As far as changing the color is concerned, there are a couple of different ways that this can be accomplished. The first method is by dying the grout. Obviously, any sealer that may have been previously applied to the grout will need to be removed so that the dye may be absorbed into the grout. On the other hand, if the existing grout is dark, and you wish to change to something considerably lighter you may be forced to remove the surface of the existing grout and replace it with new grout. A trip to your local hardware store or home improvement center will get you what you need to perform this relatively simple task.