Temporal variability of dark-sky components measured from the twelve dark exposures of the 2024 February 8 observing sequence shown in Figure 1, using individual KCWI-blue and KCWI-red exposures. The blue and red continua exhibit correlated variability at the ∼1%–2% rms level, indicating stable large-scale background conditions. The OH emission lines at λ7340.9 and λ7358.7 show coherent variability (∼2% rms; ∼8% peak to peak), consistent with common-mode fluctuations within the mesospheric OH emission layer. In contrast, the atomic [O I] λ5577 line exhibits a monotonic decline of ∼34% over the ∼70 minute sequence, evolving independently from the OH emission. This decoupled behavior reflects the distinct excitation mechanisms and atmospheric layers responsible for molecular and atomic airglow emission.