Melt and pour soap bases will not discolor on their own, however, depending on what additional ingredients were added to your soaps, those ingredients could cause a reaction that affects the color. Different fragrances, especially, can have different natural colors that will cause soaps to be darker when combined.  Fragrances that have a lot of vanilla, florals, or citrus tend to be the most likely to turn your soap darker and this can happen in melt and pour soaps or cold process soaps. You can see the vanilla content listed under the properties section on each fragrance page as a reference.

Often, it is helpful to do a small test soap when working with a new fragrance to see how it will affect the color of the finished soap. You can then use that color change to incorporate it into your soap or decide how to add dye to the soap to help mask it as needed. You can incorporate the color change into your soap by adding some swirls with a bit of unfragranced soap base to give a colored or white contrast or you can use some unfragranced white or colored soap base as embeds or layers within the fragranced to help design so the bar is not a solid brown.