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The colors, line types and line weights of all entities are almost always defined by the layer the entity is on.

For example, if an entity is on a layer called 'labels' and the color of that layer is set to 'yellow', all entities on that layer (i.e. all labels) are shown in yellow.

The same is true for hatches. So if you want to create a hatch that represents a wall, you would put it on a layer called 'walls' and make that layer for example gray.

The reason behind all this it that entities with the same functionality are typically shown in the same color to make that functionality visible to the viewer of a drawing. This is a simple floor plan with a couple of examples for typical layer uses: You can control and add layers using the layer list: View > Layer List In this example, several layers with different colors and other attributes have been added. The current layer is red and called "center lines". As long as this layer is active, all entities drawn will be red. If the color of the layer is later at any point changed, all entities on that layer will also change their color.

Keeping in mind all of the above, it is also possible to assign individual colors to entities. The easiest way to do so is by assigning a color using the property editor as shown below. Select the entities you want to change, make sure the property editor is shown (View - Property Editor) and change the color in the property editor.

In the interest of keeping a drawing well organized and maintainable, individual colors should be used very sparingly in truly exceptional cases only.

Troubleshooting

Black and White

In older CAD files, there used to be only one color for black and white. Depending on the background, that color was displayed as white (on a black background) or as black (on a white background).

To make sure a drawing is visible, QCAD automatically displays white lines as black (on a white or bright background) and black lines in white (on a black or dark background).

In some situations, you might want to be able to force entities to be black, even on a black background or white on a white background. If that is the case, you can switch off the auto color correction under:
Edit > Application Preferences > Graphics View > Appearance > Prevent white on white / black on black display