Note that, although the resolution of the HP DesignJet 1055CM is 600dpi, you should create your graphics at 300dpi rather than 600dpi. The result will look just as good, and you will avoid problems caused by the huge job sizes of 600dpi graphics. On the other hand, if you have created graphics at screen resolution (usually 72 or 75 dpi), they will not look good when printed, no matter how high the resolution of the printer or plotter.
Solid backgrounds use a tremendous amount of ink, and there is no guarantee that the result will be satisfactory. If your plot is large and has a solid color background, you may not like the result due to the saturation of the paper. It is also possible that the plotter might run out of ink before finishing the plot.
For many reasons, it is difficult to impossible to make your plotted output match the colors you see on the screen. For starters, monitors and scanners are based on an "additive" color system, using the RGB (red, green, blue) color space, while the plotters are based on a "subtractive" system and use CMYK (cyan, magenta, yellow, black). And different monitors can vary in many ways, including calibration, variances in the phosphers and bit depths. Also the device gamut (range of colors) is widely different, with monitors displaying many more colors than any printing device. Colors will also look different on different types of paper. Color science is exceedingly complex-- way beyond the scope of this discussion. Although the next section on configuring the plotter device driver and the section on plotting from Photoshop have a few tips for improved results, the bottom line is that you cannot expect exact agreement between your screen and the paper. If precise color rendition is important to you, consider going with a professional printing outfit.