If you'd like to change the colors of the bars or candlesticks in TOS, you can do so using the Appearance tab within the Chart Settings dialog.
Open Chart Settings by clicking on a chart, then clicking on the gear icon, or using CTRL+s. Select the Appearance tab. From the Chart type pulldown menu, choose the bar type you want to adjust. In the image below, Candle is selected, though you could choose Bar, or any of the other available bar types.
Just below the pulldown menu, you'll see the bar components whose colors you can adjust. For example, with candles, you can adjust the border of the color for up candles, and down candles separately, with the Border up and Border down choices. Click on the color swatch to the left of each to adjust the colors. From there, you can click any of the available colors that appear, and if you'd like more choices, click the More... button for additional selections. The chart image at the right shows how your selections will appear.
The candle settings also includes a doji color that can be used to identify those types of candlesticks with a different color.
Beneath that, you can select the colors for Fill up, Fill down for the fill colors for candles that close up or down. There's also a checkbox before each of these that allow you to optionally make them hollow by unchecking them.
Beneath that is the option to show wicks.
Once you've adjusted it to your liking, click Apply to apply the settings, then OK to close the dialog box. Or just click OK to both apply and exit the dialog.
For bars, and other chart types, you'll find similar setting controls that apply to that bar type.
If you want to return to the default colors, you can click the Reset to chart defaults button at the bottom left of the dialog.