We present preliminary filter transformations between Roman/WFI and other near-infrared photometric systems, including JWST/NIRCam, HST WFC3/IR, and 2MASS. These transformations are derived from synthetic photometry of four empirical spectral libraries, which together span nearly the full HR diagram and sample stellar populations from the solar neighborhood out to the Magellanic Clouds, covering a broad range of ages, metallicities, and other relevant stellar properties. In addition to global color-dependent transformations, we examine band-to-band differences for cool, luminous giant stars in particular. Theoretical atmospheres are known to have difficulty reproducing observed SED features for such stars due to their complex and variable atmospheric physics; therefore, empirical spectra are required to constrain their behavior.