When you create a contour map in Surfer and fill the contours with a colormap, the colormap is applied between the z minimum and z maximum values of the grid file, so it's likely that a specific color in one map is not associated with the same value that that color represents in the other map. This is easy to fix though. To change the colormaps so they're using the same numeric ranges:

1. Select one contours layer in the Contents window.
2. On the Levels page in the Properties window, make note of the Data range at the top.
3. Select the other contours layer in the Contents window.
4. In the Filled Contours section, click the ... button in the Fill Colors field.
5. In the Colormap Editor dialog, type the smaller of the two data minimums (from steps 2 and 4) into the Minimum box, and type the larger of the two data maximums (from steps 2 and 4) into the Maximum box.
6. Click OK.
7. With the Contour layer still selected, click Home | Clipboard | Copy Format. 
8. Select the other Contour layer and click Home | Clipboard | Paste Format. 

Updated December 2, 2022