In my observation, Blue Pillers take a rational approach to relationships, while Red Pillers take an emotional approach to relationships. Accordingly, Blue Pillers prefer communication, since information helps rational actors. Red Pillers prefer demonstration, since demonstration excites the emotions. By these definitions, Blue Pill is certainly not "everyone who is not Red Pill": most people have some mixture of these attitudes.

Power Differences
Blue Pillers see a relationship as a contract between two self-interested parties for their mutual benefit. They are therefore suspicious of relationships with a power difference, since they interpret those as unequal contracts, where one party will inevitably exploit the other. Red Pillers tend to favour male-led relationships, with a clear power difference, because claiming and surrendering power are both intensely erotic. As for female-led relationships, Blue Pillers are less concerned about those because they run against the grain of culture ("patriarchy"), so there's less scope for exploitation. Red Pillers disdain those precisely because they run against the grain of culture, and as they believe, biology. Among other reasons, Red Pillers claim that few women are interested in that, so it's not in a man's interest to cultivate submissiveness.

If there are problems in a relationship, Blue Pillers prefer to discuss them, to avoid misunderstanding, to obtain an optimal and consensual plan of action. Red Pill men prefer to fix them, since that is the man's responsibility in a male-led relationship.

Frame & Game
Red Pillers seem to take a somewhat perspectivist approach to social reality. What Nietzsche called a perspective, Red Pillers call a frame, an interpretation of the world that best suits their needs. To Red Pillers, game is the art of creating and demonstrating a healthy and "congruent" inner frame -- and therefore actually becoming the person they want to be. To demonstrate is to become. To do is to be. [insert Sinatra joke]

To Blue Pillers, game is a set of behaviourist tricks that take advantage of human psychology to emotionally manipulate someone to act against their own interest. Framing is one of these tricks, deliberate self-serving bias in communication that distorts objective truth, akin to deception. Mere flirting, however, is good, because that's simply a form of communication (whereas to Red Pill, game is flirting "done right").

On the extreme of Blue Pill are those somewhat Aspergerish folks who complain about ambiguity in flirting, since that ambiguity is part of its demonstrative content, at the expense of clear communication.

Should a man ask before kissing a woman?
Blue Pillers say yes, he should get consent, because there's no down-side in asking about a preference and a big down-side in not doing so. Red Pillers say no, because by kissing without asking he demonstrates the ability to read a woman's emotional state and confidence in that ability, both of which are arousing. And there is little down-side, at least for him. A brief search of the internet seemed to reveal that most women prefer not to be asked, though you can do your own research.

Attraction
Why are people attracted to others? Specifically, why is a woman more attracted to one man than another? According to Red Pill, a man becomes desirable by demonstrating desirability ("higher value"), including such things as social status, emotional stability, physical and mental health etc. For example, confidence demonstrates emotional stability and social status. Humour demonstrates social intelligence and perhaps mental health. Any kind of social proof demonstrates desirability by, well, demonstrating being desired.

By contrast, Blue Pillers focus on factors more easily understood rationally, such as compatibility of interests and values. Beyond that, they tend to treat desire as just a given, its causes a kind of black box beyond rational understanding. If someone does or does not desire you, you should simply accept that and not attempt to manipulate it.