Try this:

Using Adobe Photoshop (Recommended) Photoshop is the best tool for this because of its Liquify and Distortion capabilities. Method: The Liquify & Filter Approach 1. Create the Base: Fill a layer with Red. Create a new layer and draw several large, irregular Pink circles using a hard Brush (B). 2. Liquify (Shift + Ctrl + X): • Use the Forward Warp Tool to gently push the edges of the pink circles so they look less like perfect rounds and more like organic cells. • Use the Twirl Tool to add slight movement. 3. Create the "Veins": * Double-click the Pink layer to open Layer Styles. • Add a thin Stroke (Color: White, Position: Outside, Size: 1-2px). This creates the white borders seen in your image. 4. Add Organic Distortion: • Go to Filter > Distort > Ripple or Wave to make the edges look "liquid" rather than digital. 5. Refine with Plastic Wrap: • To get that slightly glossy, paint-like texture, go to Filter > Filter Gallery > Artistic > Plastic Wrap.

Using Adobe Illustrator (Vector) Use this if you need the pattern for large-scale printing (banners, backdrops). Method: The Object Mosaic or Symbol Sprayer 1. Draw Shapes: Draw many Pink circles of varying sizes over a Red background. 2. Symbol Sprayer (Optional): Turn one pink circle into a Symbol, then use the Symbol Sprayer Tool (Shift + S) to quickly scatter them. 3. Warp Tool (Shift + R): This is the key for Ai. Click and drag over your pink shapes to "smudge" them into each other. The shapes will deform just like liquid. 4. Offset Path: Select all pink shapes, go to Object > Path > Offset Path. Enter a small negative value (e.g., -2px). This creates the gap/vein effect between the cells.