The Origami Forum

I keep seeing people saying different things about which color goes to which parity... Personally, I use red for mountain and blue for valley, but I've had a couple of people try to correct me in the past. There hasn't been much standardization or agreement on the topic, so I thought maybe we'd try and decide, once and for all. Please read my reasons, then vote in the poll!

It's often been said that from a practical standpoint, this doesn't really matter, because the two are interchangeable depending on which side of the paper faces up. But I think it's important-- for asymmetrical designs, the crease pattern should produce a model with the intended chirality; and if the creases are in the wrong direction, we'll get a left-handed model instead of a right-handed one. Also, often people will assume that the crease pattern is viewed from the top or front side of the model, if there's a clear correspondence to that, so when we draw a CP we should be setting them up to get what they expect. The crease pattern is conceived as an orientable surface, and therefore the parity of the creases is not interchangeable and shouldn't be ambiguous.

Here's a list of reasons why I feel the colors I use are more appropriate:

• Red is a bright, active color, and pops out at you, especially on a computer screen; mountain creases are more visible on a sheet of paper, and drag the paper forward towards the folder. Blue is a calm, low-key color, and valley creases are less visible on a sheet of paper, and recede from the folder. So from a visual standpoint, it makes sense.
• Red light has a longer wavelength; "redshift" is the phenomenon where light waves are stretched towards the red end of the light spectrum because their source is moving. The opposite term is "blueshift" in astronomy. The fibers on the mountain side of the paper stretch apart; the fibers on the valley side are compressed. Red/mountain and Blue/valley would be consistent with existing scientific terminology.
• Mountains have a ridge of rocks on the top; valleys have a river running down the middle. Rocks are represented by brown or gray, and water is represented by blue, in all cultures I'm familiar with. Mountains can also be volcanoes, which are definitely associated with red. Seems like the colors should match up.

Any dissenting opinions?

I agree with you that red should be mountain and blue should be valley, but I think the problem is that some designers draw their crease patterns from the white side of the paper rather than the color side (Hojyo Takashi for instance,even though he does not use color in CPs, it is just the first author I thought of that does this) or vice-versa, so sometimes that is why the colors are reversed, making this all the more confusing.

Besides the cientific point of view, I think this is very subjective and personal likings are involved. Lang uses black instead of blue in ODS and in some CPs kamiya uses diferent weight strokes to diference mountains form valleys.

For me any way is good

I'd go for the blue = valley and red = mountain thing but also white side up should be stated next to the CP or agreed upon.

I always preferred red for valley and vice-versa, because... I don't know, it's just order/organization I guess. That's a great post about it there.

I oftentimes find some people make their crease patterns in all black, saving them all this confusion.

Yes, I generally assign black to mountains and black to valleys. On a more serious note: red-shifts as an argument for crease parity color assignment? Really? There is a vague connection there, but come on-that is a stretch. I don't feel like color usage in this case matters much-if a folder is going to fold a CP (in most cases), either they are primarily concerned with learning and structural analysis, are practicing to fold a nicer version with nicer paper (in which case they will learn how to orient the paper/CP by folding this version), or are skilled enough to recognize how the paper should be oriented by pre-analyzing the CP.

the arguments for both sides are pretty weak anyway and cp's are just as understandable if the colour of the creases is red or blue for mountain- just start with the other side up. So, really as long as people make sure that their crease patterns are flat foldable, I really don't care if it's blue for mountains or valleys or whatever.

Besides the cientific point of view, I think this is very subjective and personal likings are involved. Lang uses black instead of blue in ODS and in some CPs kamiya uses diferent weight strokes to diference mountains form valleys.

Let's not drag Lang into this. His CP's often have 4 or 5 different colors.

i usually use blue as mountain and red as valley because when i print out the cp my eyes go to blue because it is darker and usually if a cp is written with thick lines as mountains and thin ones as valleys.....