The Tower of London is an iconic landmark that has been around since the 11th century. It has served multiple purposes throughout its long history, most notably as a royal palace, a prison, and a place of execution. Today, the Tower is one of the most popular tourist attractions in London, and it is a UNESCO World Heritage Site.
To color this historic landmark, I recommend using a variety of different shades and hues of blue and grey to capture the classic aura of the castle. Start by using a light blue to color the walls and towers, then a medium blue for the rooftops and turrets, and finally a deep navy blue for the shadows. To add a bit of contrast, light and dark shades of grey can be used for the windows and doors. Finally, you can include small pops of color to give the scene even more life and vibrancy, such as light yellows for the hills and greens for the trees.