Question

how does the type of metal used for anode affect the X-ray spectra

Answer 1

The emission spectrum is determined by the transitions of electrons from external non-valence shells to existing (previously created) vacancies in the internal electron shells of the atom. The energy of the photon emitted during the transition (i.e., its frequency) depends on the magnitude of the charge of the atomic nucleus, i.e. on the type of metal (Mosley law).