If you're adding data using a mySidewalk layer and it looks blank besides the sub-geography outlines, the data probably isn't available for the sub-geography you're using.
To fix this, choose the next highest geography. For example, if you were looking at census block groups, change the sub-geography to census tracts.
If the data is available for the new sub-geography you chose, the map will change from blank to filled with one color. To see how the data varies across your main geography, increase the number of data bins.