Yes, you can definitely change the color of specific bars in an Excel bar graph. Here's how you can do it:

1. First, select the data series that you want to change the color for. You can do this by clicking on any bar in the series. This should highlight the entire series.
2. Once you have selected the data series, right-click on it and select "Format Data Series" from the drop-down menu.
3. In the Format Data Series pane that appears on the right-hand side of the screen, click on the "Fill & Line" tab.
4. Under the "Fill" section, you will see a color palette. By default, the bars will be set to the "Automatic" color option. To manually assign a color to the bars, click on the "Solid fill" option.
5. Once you have selected "Solid fill", you can choose the color you want by clicking on the color palette or by entering the RGB values for the color you want.
6. Repeat steps 1-5 for each data series that you want to change the color for.
7. If you want to change the color of individual bars within a data series, you can do this by selecting the specific bar you want to change and then following steps 2-5.

That's it! By following these steps, you should be able to manually assign different colors to the bars in your Excel bar graph.