Fill Effects

I'm working on a pricebook, many worksheets. On all worksheets, I'm using
the fill color option on the headers (gray 20%). They all look solid, no
pattern applied. However, when I print everything out, a couple of the
worksheets print those header cells with a patterned look. It still looks
like it is supposed to on the monitor and the settings I find say no pattern
is applied. How do I stop this? I would like all the header cells to look
uniform, solid not a patterned look.

Some printers cannot print a solid 20% grey but instead achieve the 20% by using a dotted pattern (like an old newspaper photograph). Try a temporary change to 40% grey and see if the pattern becomes solid.