We investigate the problem of maintaining the arc labels in the suffixtree data structure when it undergoes string insertions and deletions. In current literature, this problem is solved either by a simple accounting strategy to obtain amortized bounds or by a periodical suffix tree reconstruction to obtain worst-case bounds (according to a global rebuilding technique). Unfortunately, the former approach is simple and space-efficient at the cost of attaining amortized bounds for the single update; the latter is space-consuming in practice because it needs to keep two extra suffix tree copies. In this paper, we obtain a simple real-time algorithm that achieves worst-case bounds and only requires small additional space (i.e., a bi-directional pointer per suffix tree label). We analyze it by introducing a combinatorial coloring problem on the suffix tree arcs.