There's a lot of options for filling the windows with color. You could leave yellow as is. You could put in some lace curtains, cafe curtains or window shades. You could fill the window area with shades of blue, light gray or dark gray to indicate interior lights on or off and put some flowers or people in the window. Or you could attempt what I call the 'candle glow' seen in many popular cottage paintings. It's your choice. Decorate the windows any way you want!
Candle Glow
To create the candle glow in the windows, we will use the 4 colors in the 'candlelight' swatch to paint arcs of color in the yellow rectangle. Sort of like a rainbow. To make a gradual transition between colors that replicate the candle glow, we will add alternating pixels (check pattern) to blend the colors. Starting at the top, paint a few rows with first color on left, then about 6-10 rows with a check pattern made with color #1 and #2, then 6-10 more rows of checks made with color #2 and #3. Finally rows of checks are made with color #3 and #4 with a few rows of just color #4 to finish the window. Complete one window before doing other windows. When that window is done, copy and paste it behind the other 4 windows. (Turn visibility of HOUSE layer back on, but do all copy/paste on WINDOW layer.)
Speed Tip: Paint 4 arcs of color using the 4 colors form the candlelight swatch, like a rainbow as described above. Next, make check patterns as separate images (about 6x6 pixels). Make a new image for the first 2 colors, one with the 2nd pair of colors and a new image with the 3rd pair of colors. Use these images as pattern fills. On the WINDOW layer of the cottage, select the top arc of the 'rainbow' with the Magic Wand and flood fill it with the check pattern made from color #1 and #2. Then select the next section of color and flood fill it with the next pattern, then the 3rd. Go back and paint over some of the check pattern at the top with solid color #1 for a few rows. Paint over some of the check pattern at the bottom with solid color #4. Touch up where needed. Copy/paste for other windows.
Are you tired of fiddling with the house construction yet? I am! Take a break. Next step we'll start planting some trees and flowers! Turn visibility on for all layers and de-select any marquee that may be active.