minor doc fix for microsoft#921

docs/image_apis.md

@@ -204,7 +204,7 @@ The `getCameraInfo(camera_id)` API call returns pose (in world frame, NED coordi
 You normally want to retrieve the depth image as float (i.e. set `pixels_as_float = true`) and specify `ImageType = DepthPlanner` or `ImageType = DepthPerspective` in `ImageRequest`. For `ImageType = DepthPlanner`, you get depth in camera plan, i.e., all points that are in plan parallel to camera have same depth. For `ImageType = DepthPerspective`, you get depth from camera using a projection ray that hits that pixel. Depending on your use case, planner depth or perspective depth may be the ground truth image that you want. For example, you may be able to feed perspective depth to ROS package such as `depth_image_proc` to generate a point cloud. Or planner depth may be more compatible with estimated depth image generated by stereo algorithms such as SGM.
 
 ### DepthVis
-When you specify `ImageType = DepthVis` in `ImageRequest`, you get an image that helps depth visualization. In this case, each pixel value is interpolated from red to green depending on depth in camera plane in meters. The pixels with pure green means depth of 100m or more while pure red means depth of 0 meters.
+When you specify `ImageType = DepthVis` in `ImageRequest`, you get an image that helps depth visualization. In this case, each pixel value is interpolated from black to white depending on depth in camera plane in meters. The pixels with pure white means depth of 100m or more while pure black means depth of 0 meters.
 
 ### DisparityNormalized
 You normally want to retrieve disparity image as float (i.e. set `pixels_as_float = true` and specify `ImageType = DisparityNormalized` in `ImageRequest`) in which case each pixel is `(Xl - Xr)/Xmax`, which is thereby normalized to values between 0 to 1.