Help with colorspace on MacBook for printing comics

Because you mentioned a MacBook Pro, P3, and D50, are you actually asking about the P3 Presets in System Settings / Displays, and not about profiles in Photoshop? If so, are you asking about the P3 presets I marked in the picture below?

If that’s what you’re asking about, this is an area widely misunderstood by many Mac users because it’s relatively new. Those are definitely not profiles and should never be called profiles, to avoid confusion with the ICC color profiles used for display, editing, and printing. These are reference mode Presets and are an entirely different kind of thing altogether. And they do not replace ICC profiles, but work together with them.

This is what they are for:

Design & Print (P3-D50) and Photography (P3-D65) can be appropriate for print, because of their maximum luminance of 160 nits. Choose the one with the white point that your printing company tells you is a closer match to their viewing booth for print proofing. But I think a lower display luminance is more appropriate for print, so I used the Customize Presets command to copy one and lower its Maximum Luminance to where I like it. 

Apple XDR Display (P3 - 1600 nits): This is best for viewing and editing HDR photos/video. Not recommended for previewing for print, because the dynamic range vastly exceeds what any printer ever made can reproduce.  

Apple Display (P3 - 500 nits): This is kind of OK for print if you’re fine with a D65 white point, but the maximum luminance is a bit bright for print. If you dial it down to around 90-120 nits using the Brightness controls, that would work a little better for print. 

Digital Cinema (P3-DCI) and (P3-D65) should only be used for editing video to be shown in cinemas because of the extremely low maximum luminance of 48 nits, which is how dim it can be in a movie theatre. The only difference between these two is the white point.

Reference mode presets are not some kind of weird Apple thing. They are similar to the hardware calibration presets that have been in use in high-end displays for many years. They constrain the hardware behavior of the display from its native calibrated state, unlike an ICC color display profile that the operating system uses to apply a calibration in software.

P3 will work fine for general process color print reproduction. Some will prefer Adobe RGB because that fits CMYK slightly better, but if you’ll be editing on your MacBook Pro display, Apple display panels are natively P3.

Apple includes display profiles specifically for your MacBook screen. Absent hardware calibration, these profiles are typically pretty close. So use the system matching profile for your internal screen. If you have an external display, again look for a matching Apple-supplied profile that matches the display model.

Printing is usually darker than video or display, so factor that in when you are designing graphics. Comic books are often printed on cheap uncoated paper and have a simple color gamut. I would ask the printer for their preferred colorspace and printer profile if they have one, otherwise sRGB or AdobeRGB are probably both fine.

If I was worried about accurate color on press, I'd do a sample sheet with common elements including text and pay for press proofs. See how an actual press run looks on paper.

The display profile (the p3 profiles) and the document profile are two different things, serving different purposes. Do not use the display profile as document profile. That defeats the whole purpose of color management.

The purpose of the display profile is to be an accurate description of the display's actual and current behavior. So you use whatever system display profile is the closest to how your display actually represents the numbers. Having one made with a calibrator, based on actual measurement, would be much better. 

The document profile needs to be a standard color space, traditionally, sRGB, Adobe RGB or ProPhoto. However, it has become increasingly common in the Mac community to use Display P3 everywhere - not really what P3 was intended for, but given that this is becoming common practice, Display P3 should be included in the list of standard profiles.

Next, to get a preview of what the file will print like, you proof to the print profile. The printer will need to tell you what their print profile is. It sounds like this is going to be printed on an inkjet printer, not offset, which is why they're asking for RGB and not CMYK.

The purpose of proofing is to show you on screen what colors in the file are out of the printer's gamut. It restricts the on-screen representation to the gamut of the print profile. Ultimately, the printed result is limited by the physical properties of the specific inks on the specific paper, which is reflected in the profile. If it's a high-end inkjet printer, you may not see a very dramatic difference. If it's offset, expect a severe dulling down of many strong colors.

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That was the color management part. There's a second part, which is display calibration - white point color and luminance, and black point. Monitor white should be a visual match to paper white, and monitor black should match max ink. This is a purely visual match - if it looks right, it is right. Most displays out of the box are way too bright and with much too high contrast (too deep blacks).

Since you don't have a calibrator, numbers won't tell you anything. Just adjust brightness until it looks right. If you get it right, what you see on screen will match the printed result.