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Transitional millisecond pulsars (tMSPs) are rare neutron-star binaries that switch between accretion-powered and rotation-powered states, offering a valuable laboratory for studying the coupling between accretion flows, magnetospheres, and pulsar winds. Their simultaneous optical and X-ray variability often shows complex correlated or anti-correlated behavior, but the physical origin and stability of these patterns remain unclear. In this work, we present a multiwavelength analysis of the tMSP candidate 3FGL J1544.6−1125 using three XMM–Newton observations with Optical Monitor data obtained in the U, White, and V filters. We examine the optical response during X-ray low-mode episodes using a low-mode selection and optical-ratio method comparable to that applied to PSR J1023+0038 (Ka-Yui Au et al. 2025). Although the optical emission shows a tendency toward anti-correlation with the X-ray flux, with the effect appearing stronger at longer optical wavelengths, anti-correlation statistic does not reach significance in any of the three 3FGL J1544.6−1125 observations.
Owing to the intrinsically weak optical signal, we apply Gaussian Process (GP) regression to denoise the OM light curves and enhance the detectability of variability features. It suggests that GP regression may be useful for identifying marginal anti-correlated behavior in noisy or weak optical data, including marginal cases in PSR J1023+0038, though the anti-correlation of 3FGL J1544.61125 is still statistically insignificant with GP regression. We further compare 3FGL J1544.6−1125 with confirmed anti-correlated observations of PSR J1023+0038. For PSR J1023+0038, we measure a delayed optical return following the end of X-ray low-mode episodes, with the optical emission typically requiring an additional 20-30 s to return to its non-low-mode level. The X-ray low-mode duration distributions in both systems are lognormal-like, with PSR J1023+0038 showing a longer characteristic duration, median about 80 s, compared with median durations of about 40-60 s in the three 3FGL J1544.6−1125 observations.