Pollinators are important for the evolution of flowering plants, but questions remain about how early stages of pollinator-mediated speciation arise. Studying intraspecific variation in floral traits can shed light on early stages of floral trait divergence and identify how traits evolve as signals to novel pollinators, either acting separately or in concert. Within the genus Mimulus (monkeyflowers, Phrymaceae), section Erythranthe offers replicated examples of floral trait evolution and pollinator shifts among species, as well as cases of intraspecific trait variation. Among two hummingbird-pollinated members of this section, M. verbenaceus and M. cardinalis, yellow floral morphs have arisen from more common, red-flowered morphs and have become well-established in several populations. To identify 1) whether these floral transitions involve additional floral traits beyond color and 2) if they represent incipient pollinator shifts, we characterized yellow-flowered morphs of M. verbenaceus and M. cardinalis and their more common red-flowered forms across numerous floral traits and assessed pollinator preference. We characterized floral reflectance and pigmentation, volatile organic compounds (VOCs) comprising floral scent, floral morphological traits, and nectar rewards. We then investigated how trait differences impacted behavior of a novel bumblebee (Bombus terrestris ssp. audax) pollinator by examining perception of color and scent signals and assessing preference among floral morphs in controlled experimental arrays. For floral color, the two yellow morphs show distinct hues of yellow that vary in reflectance and pigmentation and likely appear distinct to potential bee pollinators. For floral scent, both yellow forms differ from their red conspecific forms, though in contrasting ways. In M. verbenaceus, the yellow form produces a similar bouquet of VOCs but emits them at greater rates than the red morph, while in M. cardinalis, both color morphs produce little scent overall, but their composition differs markedly. In both species, yellow morphs have wider, less restrictive corolla openings, but species showed contrasting patterns of variation in corolla length, while nectar rewards varied little between conspecific morphs. Collectively, these floral trait differences resulted in a clear preference for yellow morphs over red in both species, with naïve bumblebees choosing yellow flowers at a rate of 2:1 over red. Despite the increased attractiveness of yellow morphs, bumblebees had difficulty handling flowers, especially those of M. verbenaceus, suggesting they may nonetheless be ineffective pollinators to these species. Overall, this study reveals that similar transitions in floral color in two closely related hummingbird-pollinated species may follow independent evolutionary paths and are associated with varying changes across a suite of other floral traits, with implications for interactions with novel pollinators and the potential for future pollinator-mediated floral evolution in these taxa.