Transparency of drawings after rasterize vector-based PDF

[sayvick]

Hello, I am trying to rasterize PDF which is full of drawings. I used some methods for reduce size of PDF, which appeared on other topics (many thanks for those who shared the codes!)

for page in src:
    
          pix = page.get_pixmap(dpi=DPI,annots=True,colorspace=pymupdf.csRGB)
          png = pix.tobytes('png')
          outpage = target.new_page(width = page.rect.width, height = page.rect.height)
          outpage.insert_image(outpage.rect, stream=png)

          target.ez_save(f'{dir_test}\\TEST--RASTER-OUT.pdf')

What I want to understand is when I put example PDF with drawings like this:

after rasterize I have PDF with change of drawing's colors:

What is happening? Is this something related to transparency of drawings?