In Jain Dharma, the “change of blood colour” is spoken of specially for Tirthankar Bhagwan, not for every kevali.

1. What do the scriptures say? Jain granths describe 4 special physical qualities of a Tirthankar from birth. One of them is:

• Due to extreme shānti (peace) and anant dayā (infinite compassion),

the red blood cells become white, so the flesh and blood of a Tirthankar are milky‑white and always pure, without bad smell, sweat, or disease.

This is counted as an atiśaya (extraordinary attribute) of Tirthankar‑nāma‑karma.

2. Why does it happen after Kevaljnān? In simple spiritual terms:

• When Kevaljnān arises,

- all ghāti karmas (knowledge‑obscuring, perception‑obscuring, deluding, obstructive) are destroyed. - The soul becomes sarvajña – all‑knowing, vitarāg – totally without attachment & aversion.

• For a Tirthankar, this inner absolute purity is also reflected in the body as many atiśayas,

one of which is white, pure, fragrant blood and flesh.

So the “change of blood colour” is a symbol and consequence of total inner purity and compassion.

3. Is this symbolic or physical? Traditional Jain view treats it as a real, miraculous quality given by Tirthankar‑nāma‑karma. Modern biological explanation is not the aim of the scriptures; it is a spiritual description, showing:

• No impurity, no disease
• No violence, no raag‑dvesh
• Body and mind both completely shuddha (pure)

4. Digambar / Shvetambar view

• Both accept that Tirthankars have extraordinary, pure bodies.
• Details like “white blood” are mentioned in traditional literature and accepted in Jain kathā and vyākhyā in both traditions as a Tirthankar‑atiśaya.
• The main spiritual point is the same:

Tirthankar’s body is utterly pure because the soul is utterly pure.

You can read a simple explanation on this topic here