When subtracting an integer of a different sign, the two-color counter model uses neutral pairs to provide counters of the needed color without changing the overall value.

• To compute $-6 - 4$, begin with $6$ negative (red) counters. To subtract $4$ positive (blue) counters, introduce $4$ neutral pairs. Removing the $4$ positive counters leaves the $6$ original negative counters and the $4$ new negative counters. Therefore, $-6 - 4 = -10$.
• To compute $6 - (-4)$, begin with $6$ positive (blue) counters. To subtract $4$ negative (red) counters, introduce $4$ neutral pairs. Removing the $4$ negative counters leaves the $6$ original positive counters and the $4$ new positive counters. Therefore, $6 - (-4) = 10$. This process visually illustrates how subtracting an integer is equivalent to adding its opposite.