What is this discoloration? Bruising or something else? (photos)

Although you photo is limited since you covered your areolae, it appears you have some skin pigment changes. If glue and tapes were used, you may had had an allergic reaction. Try some skin tightening creams. Later, you can try laser treatments if needed.

Hi and welcome to our forum!
From your photo, I note well healed inframammary scars (below the breasts) but broad hyperpigmented vertical and periareolar (around the areola) scars as well as an apparent notch deformity at the bottom of the left breast, suggesting the presence of excessive tension at the original closure or a healing delay after surgery. There are non-surgical modalities available to lessen the appearance of the scar (such as laser, skin bleaching, etc.) A moderate degree of success may be noted after treatment.
If a year has passed since your breast reduction (to allow for subsidence of swelling and the hypervascularity of healing), you may wish to consider revisional surgery. 15% 0f cosmetic surgeries can be improved through secondary revision.
Revisit your plastic surgeon for evaluation and discussion.
Best wishes...