The very first sentence on the color palette challenge page states: Each month, when the new color is posted, a link box will be added for the previous month’s project.
To find the links to January’s projects, click on the February link. Those blog posts are made on the first of each month and include the link box for the previous month’s submitted projects.
It’s the same way with the UFO Challenge. Each month when the new number is posted, the ink box is included for the previous month’s completed projects.