Our topographic maps are produced from multiple scanned U.S. Geological Survey maps. In some locations (and dates), the colors were been printed inconsistently by the USGS, which comes through as different colors in the scans. This causes the color shades to look inconsistent across your map.
Aerial photos come from multiple photo sources (and dates). This too will cause color shading differences between photos produced from different flights.
Simply put, it is not possible to adjust color differences across different base map (or photo) sources.