Once you have a cell color set, you can make adjacent cells the same color by clicking in the cell with the color, and then roll your mouse pointer over the edge of the cell in the direction you want to propagate the cell color. When you see a yellow dot appear on the cell boundary, click and drag in the direction of the cells whose color are to match the original cell color.
For non-adjacent cells, click in the cell with the color you want to replicate. In the Format > Cell panel, click Fill, and choose Color Fill. Click on the color globe, and use the hand lens icon to capture the original color into the color chooser. This is now the fill color. Click on the non-adjacent cell you want to color, and reselect Color Fill from the Cell panel. The cell will fill with the specified color. Repeat paragraph one as needed.
If you want to fill an entire row with the same color, click on the row number (or range of cells using the shift key) so that the entire row is selected. Then choose Cell > Color Fill and the row will be set to the specified color.