TKI drugs have side effects because, although they are targeted drugs, they are not perfectly targeted. TKI drugs target the BCR-ABL leukemic process and inhibit it, which is what we want*. But the body has numerous tyrosine kinases, and some can also be inhibited, including c-Kit and PDGFR. Sprycel additionally inhibits some SRC tyrosine kinase processes. It is this secondary inhibition of other tyrosine kinases (unintended) that are generally believed to cause the skin rashes, hair folicle problems, scalp itch, muscle cramps, etc. So the hair folicle can be disrupted by the TKI drug, probably by inhibiting cKit, which can lead to temporary hair loss. Normally the body adjusts to this over time and finds ways to reverse it, and the hair grows back. Sometimes the hair grows back in a different texture, and sometimes even a different color. When it comes to side effects, we are all different in some ways.
* Technically the TKI drugs target the ABL in BCR-ABL, and also regular ABL