We demonstrate a versatile single-laser platform for single-beam dual-color two-photon spectroscopy that combines a short-pulse laser source with a tunable broadband wavelength converter based on a highly nonlinear photonic-crystal fiber (PCF). We show that the short-pulse PCF output can be tailored, via dispersion and nonlinearity management, to deliver a broadband optical driver whose spectral structure is ideally suited for a single-beam two-photon absorption (2PA) spectroscopy of the next-generation genetically encodable fluorescent-protein (FP) sensors of pH and redox-responsive contrast agents. As a promising spectroscopic resource for redox biology, the short-pulse PCF output can be finely sculpted to alternately drive an FP system via a one of its two 2PA-allowed quantum pathways, yielding a high-contrast fluorescence readout for a highly sensitive detection of redox reactions and signaling, pH sensing, and oxidative-stress diagnosis.