Consider the following patterns of colored squares:
Courtesy: MS Paint application
I can't seem to find a word (phrase?) to describe the pattern observed in the third row.
The first row has consecutive blue squares.
The second row has alternating blue squares.
The third row has _______________ blue squares.
Does such a word describing the third pattern (preferably, in terms of "blue") exist?
Or should I use some phrase instead? And what phrase?
You can call them regularly spaced blue squares.
regularly adverb With a constant or definite pattern, especially with the same space between individual items. ‘regularly spaced buildings’ - ODO
Note that talking about regularly spaced blue squares says nothing about the order of the red and green squares.
Here's an example of the term used in the context of having other things in the spaces between pairs of regularly spaced pixels (emphasis, mine):
Applying spatial offset, the green sensor is moved one-half pixel out of alignment with respect to the blue and red targets. The strategy is intended to capture detail that would otherwise fall inside the grid, i.e. between the regularly spaced pixels. - Video Shooter: Storytelling with DV, HD, and HDV Cameras by Barry Braveman
The third row has a repeating pattern of blue, red and green squares.
You just have to determine what the pattern is (in your example blue-red-green).
Unfortunately you can't "describe the pattern observed in the third row" by only mentioning the blue squares.
Edit:
Based on your comment, if we are considering only the blue squares (the others being irrelevant), you might say:
Every third square is blue.
There are a couple words that can be used to describe the pattern on the third row:
Array: An ordered series or arrangement. "The array of blinking green lights flashed happily in the darkened server room."
Series: A particular order in which related events, movements, or things follow each other. "The series of colored boxes followed a regular pattern of blue, red, and green."
