We explore the use of tailored resonant waveguide gratings (RWG) embedded in a glass-like matrix as angularly tolerant tri-band reflection filters under oblique excitation. Through inverse design we optimize 1D grating structures to support multi-frequency narrowband resonances in an otherwise transparent background, ideally suited for augmented reality applications. In particular, we show theoretically and experimentally that a single RWG can be tailored to provide reflection levels larger than 50% under p-polarized excitation at three distinct wavelengths of choice, over a narrow bandwidth and within a substantial angular range around 58° incidence, while simultaneously eliminating ghost reflections from the glass/air interface. Similar performance can be achieved for s-polarization by cascading two RWG's. Moreover, we demonstrate that these metrics of performance are maintained when the devices are fabricated using roll-to-roll techniques, as required for large-area industrial fabrication. Overall, these devices show exciting potential as large-area transparent heads-up displays, due to their ease of fabrication and material compatibility.