SolidWorks has many default colors for different types of dimensions. On drawings, the two main types of dimensions are inserted (driving) and non inserted (driven). Inserted dimensions are called such because they are inserted from the model. Non inserted dimensions are created within the drawing itself. Many times both are necessary on a drawing. By default, they appear as two difference colors. Inserted dimensions are black and non inserted dimensions are grey, by default.
These colors carry over to printouts while in Color Display Mode is on. When this mode is turned off, all colors are shown as system status (system defines the color based on their status instead of other settings). So, many users rely on the Color Display Mode. When this mode is turned on, the user gets their colors right for other lines, but dimensions appear as both black and grey. This may be not be desirable for some situations.
So, here's a quick trick to address the need to have dimensions appear the same. Simply change the color for non inserted dimensions within the System Options. What color to use? Well, if one still wants to know the difference between inserted and non inserted dimensions when editing the drawing, I recommend not picking black. Instead pick the darkest grey available. This will allow you to see the difference within SolidWorks, but such a difference will not be obvious in any printouts or PDFs.
To make this change in SolidWorks, goto Tools pulldown>Options...>System Options>Color heading. In the Color schemes settings box, select Dimensions, Non Imported (driven). Click the Edit button. A traditional Windows color palette window will appear. Use this window to create a very dark grey color and then assign it to one of the slots in the Custom colors area. Choose that color as the setting and click OK to exit. Then click OK in System Options to implement the change.
All inserted dimensions will continue to be black, and non inserted dimensions will now be that dark grey. Since this is System Options setting, it affects any drawing that is opened without having to enter the Document Properties area every time.