As disability is understood to be biopsychosocial, there is a related design trend in the assistive technology industry towards products whose appearance can be customized, particularly for children. Considering these developments, an opportunity was identified to create an add-on product that customizes children’s prosthetic blades. The purpose of this thesis project was therefore to explore the customer needs for an add-on product that offers appearance customization for children’s prosthetic blades, and to design a concept that achieves such needs. To do so, two main research questions were explored consecutively utilizing a Double Diamond design process and a design thinking framework. The first research question was “what are the customer needs for an add-on product customizing the appearance of children’s prosthetic blades?”. It was explored using semi-structured qualitative interviews with four Certified Prosthetist Orthotists (CPOs), and two parents of children who wear prosthetic blades. A thematic analysis was used to analyse transcribed text and group key themes. The analysis was used to generate customer needs statements, personas, a mood board, and a design brief that defined the needs. The second research question was “how can an add-on product that customizes children’s prosthetic blades be designed to meet the customer needs?”. It was investigated by developing several product concepts using brainstorming and sketching. The concepts were then evaluated using a Weighted Objectives Matrix, prototyping, and a mixed-methods convergent-parallel survey filled out by five CPOs, four parents, and one wearer of prosthetic blades. The results informed the best concept to be adapted and developed: an adhesive concept called “Dash in Colour”.