The canvas is primed in white and this colour shows through along the edges of the canvas, which Rothko deliberately leaves clear. There is also a narrow stripe through the middle which he leaves free from the blocks of colour which are placed on either vertical side of it. The bottom half is dominated by a bright blue colour that stretches out to the edges of the composition, just leaving a few inches free. The borders are rough and imprecise, not even straight which was entirely the way that he worked during this period. The upper half is in two tones, with a larger bright yellow, with red underneath. The red was clearly added at the end, as elements of yellow show through from behind, and also mixed in with the red in some places.
Rothko developed this style after years of trying out different methods, many of which you would not immediately recognise as his own. This is entirely typical of many modern artists, who would fill their early years with experimental work as they sought to find out both what they were good at, but also what most interested them. Those with a limited knowledge of some of these artists will only have come across the work in the movement in which they were best known, but there is often an awful lot else to see and enjoy too. Some examples of this would be European painters Joan Miro and Piet Mondrian, who became more and more abstract over the course of their careers, but left behind an impressively varied oeuvre that more and more are now becoming aware of.
This piece, titled Untitled (Yellow, Red and Blue), was produced on a very large canvas which allowed the colour choices to essentially overwhelm your senses. The way in which they were displayed would be carefully managed by Rothko when setting up his exhibitions as he wanted to get the experience just right. Once these items had entered private hands, then of course his control was completely lost but that is one of the downsides of being a successful artist and most others would just be grateful to be able to find buyers for their work. The high prices that Rothko's paintings have enjoyed occurred after his passing, and so he will never have known of the extraordinary sales that have been held at major auction centres, particularly over the past two decades.