I don't think this can be done in Lightroom with much success. You'd be much better off using Photoshop or Photoshop Elements.
That's what I thought. Thank You!
PS gives you many more options using layers, but it can be done in LR.
1) Set the Zoom view as large as possible to contain the area being colored.
2) Select the Adjustment Brush and set the 'Color' swatch to the Hue and Saturation you want to use.
3) Set the brush Size, Feather, and Flow until you find settings that work well. Density at 100 is probably best.
4) Try using the Auto Mask setting if the area being filled is even-toned and surrounded by darker or lighter areas.
5) If you accidentally color outside the target area hold down the ALT key to switch to Erase mode, adjust brush size smaller if necessary, and clean-up.
You can also create a B&W image using an original color image and only show color in specific areas. Here's an example: