To explain the link given by GH from MO (simply because it may die): Essentially, the computations required to make the proof are known, but their complexity grows exponentially* with increasing $d$. The complexity thereby outruns the capacity of our computers to date at a relatively small value of $d$.
*Accirding*According to comments (Terry Tao), known algorithms have doubly exponential runtimes, that is $a^{b^d}$ where both $a,b>1$ and the red/blue number is $d$.