Hello tazzo,
The channels in the provided files are not marked as Red, Green, Blue, therefore Metashape shows only the first band in grayscale.
Also it seems that the channels are Y, Cb, Cr (at least according to information derived by ExifTool), so you need to use Raster Calculator in Metashape with appropriate formulas and False Color palette to display the images in RGB space.
But probably it would be easier to save the TIFF files in RGB space, so no additional operations are required in Metashape. Please also specify, what applications you use that display these images properly by default.