CMYK and RGB

Yep, PNG is an onscreen format, it doesn’t support CMYK colour spaces.  Also, if you plan to work in. CMYK, better ask the printer what CMYK ICC profile to use, CMYK is not universal, by a long chalk.

Additionally, it's worth mentioning that most logos are designed as a re-scaleable Vectors in an application such as Illustrator. If you allow the text (is there text included?) to be rasterised then you've lost the ability to scale it up and down nicely. Follow this link for Best Logo Design, Adobe Software.

If you do want to use Photoshop, follow this link for How to Design a Logo with Adobe Photoshop

I hope this helps
neil barstow, colourmanagement net - adobe forum volunteer - co-author: 'getting colour right'
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Also, CMYK is strictly for commercial offset printing. You really need to know what you're doing! There's a thousand ways to ruin a CMYK file so that it can't be used. CMYK is for experienced users.

Work in RGB and keep your master files RGB. Convert to CMYK only if and when needed - and not before you know which CMYK profile is appropriate for the printing process.

PNG doesn't support CMYK mode as it is intended for monitor/device display. When you export to PNG you may or may not lose the resolution metadata and the 300 ppi image may be reported by other software as 72 or 96 ppi.

PNG doesn't even use ppi, the sizing is based on pixels per metre, which is translated on the fly by apps to a rounded pixels per inch value:

11811 ppm or 118.11 x 2.54 = 299.9994 ppi, rounded up to 300 ppi.