Colony-forming unit (CFU) assays are a powerful tool in hematopoietic research because they allow researchers to functionally test the lineage potential of individual stem and progenitor cells. Assaying for lineage potential is important for determining and validating the identity of progenitor populations isolated by methods such as fluorescence-activated cell sorting (FACS). However, current methods for CFU assays are limited in their ability to robustly assay multipotent progenitors with the ability to differentiate down the myeloid, erythroid, and megakaryocytic lineages because of the lack of specific growth factors necessary for certain lineage outputs. In addition, manual counting of colony types is subjective resulting in user to user variability in assessments of cell types based on colony and cell morphologies. We demonstrate that the addition of granulocyte colony-stimulating factor (G-CSF), macrophage (M)-CSF, and granulocyte-macrophage (GM)-CSF into a collagen-based MegaCult medium containing IL-3, IL-6, SCF, EPO, and TPO allows for the differentiation of common myeloid progenitors into expected proportions of colonies containing granulocytic (G), monocytic (M), erythroid (E), and megakaryocytic (Mk) cells. Additionally, we demonstrate an objective method using in situ immunofluorescence (IF) with anti-CD66b, anti-CD14, anti-CD235a, and anti-CD41 to detect G, M, E, and Mk cells, respectively. IF stained colonies can be analyzed individually at a microscope or using high-throughput microscopy. Thus, our improvements to the culture conditions and method for assay readout increase the accuracy, reproducibility, and throughput of the myeloid CFU assay.