Sometimes after descreening a large solid area of halftones, there may still be a small amount of pattern left over and it would look better if it was a solid color.
This is the baseline. The blue area is descreened, but still has some noticeable pattern to it.
Select the solid color using the magic wand, be sure to set the mode to ADD so you can select on the affected letters/areas.
Next go to Select and Grow/Shrink
Use a negative number to shrink the selection on itself, so that a little less that what the color you selected is now active. This will preserve the natural transitions to the surrounding colors.
Once you have shrunken the selection, use the color picker to get the color we want to fill. In this case blue. Make sure to set the radius to something big enough to get a good average. This scan is 800DPI, so 17x17 usually good enough. Bigger sample area gets better average, but be careful it's not so big that you select other surrounding colors.
This will set the color on your color panel.
Next create a new layer on top of your current layer. This will be the fill layer. Be sure to select the new layer before adding color!
Use the paint bucket or brush to fill the selection.
The color will now be solid, but there will be an unnatural hard edge between the layers
If we put a black layer in-between we can see it better for demonstration purposes.
To soften this, we can feather the edges using Gaussian Blur. Select the layer and select Layer Effects.
Slide the Gaussian Blur slider to something that works. This is 800DPI and 1.0 to 2.0 pixels works well.
If we remove the black layer we can see how it looks.