A set of points $M$ in the plane satisfies the following conditions:
(a) No three points are collinear;
(b) Each point in $M$ can be colored either red or blue such that every triangle with vertices of the same color has at least one point of the other color inside it.

Determine the maximum possible number of elements in $M$.
Let $n(n \geqslant 3)$ red points form a convex hull $F$, among which $k$ red points are inside $F$. The convex $(n-k)$-gon $F$ is divided by diagonals into $n-k-2$ red triangles. Each internal red point further divides its triangle into 3, resulting in a total of $n-k-2+2k=n+k-2$ red triangles. According to the given condition, each triangle contains at least one blue point, so there are at least $n+k-2$ blue points in $F$ (for $n \leqslant 2$, $k=0$, this estimate also holds). Similarly, within the convex hull $G$ of these $n+k-2$ blue points, there are at least $n+k-2-2$ red points. Since $G$ is inside $F$, we have $n+k-4 \leqslant k$, which implies that the number of red points $n \leqslant 4$. Similarly, the number of blue points is no more than 4, so the total number of points is no more than $4+4=8$.
As shown in Figure 5, an 8-point set satisfies the given conditions, achieving the maximum total number of points.