Left : colour modulation of 2M1721+33 (green), 2M0036+18 (blue), and 2M1906+40 (red) compared with the sample from Lew et al. (2020b) (black circles and lines). The grey circles represent brown dwarfs with known parallaxes across spectral types, taken from the UltracoolSheet Best et al. (2024). The slopes of 2M1721+33 and 2M0036+18 in particular are shallower in comparison to the rest of the sample, showing that as these objects rotate, they become brighter and bluer. Right : 2MASS J vs 2MASS J-H’ magnitudes for each observation (dark circles are binned down to a 441-second cadence) along with the individual fits for each brown dwarf using orthogonal distance regression (ODR), with their θ values and associated uncertainties. The colour modulation plot for 2M1721+33 appears as nearly two individual regions; however, this is due to a lack of phase coverage as a result of HST observations. The two observations of 2M0036+18 are plotted separately and they have a very similar slope, even though the observations were performed 16 months apart.