(1) Background: The aim of the paper is to determine how selected staining liquids affect color stability and reflectance of six composite and compomer dental materials. (2) Methods: Six dental materials were chosen for this study: G-aenial (GC), Filtek Z550 (3M), Herculite XRV Ultra (Kerr), Compoglass (Ivoclar Vivadent), Dyract Extra (Dentsply), and Dyract Flow (Dentsply). Ten staining liquids were used (distilled water, tea, tea with sugar, coffee, coffee with sugar, Coca-Cola®, orange and currant juices, soy sauce, and wine). Staining was carried out at 37 °C. The measurements of the color difference (ΔE) and the color parameters were carried out on a Konica Minolta CM5 spetrocolorimeter at different staining times (1, 2, 4, 8, 24, 48, 72, and 168 h). The resulting color change of the dental materials upon staining is presented as plots of ΔE, diffuse-reflection spectra, and Maxwell’s triangle. (3) Results: Significant changes in lightness (ΔL) along with changes in the total color were observed for most materials. Color change was more pronounced in compomers than in composites. (4) Conclusions: Most materials change their color from light cream to light-brown and reddish after exposure to selected staining liquids.