I am designing a timeline in which about ten repeating events on the line are colored. My problem is that no combination of colors look good. When laid out like I have it. I've tried different shades of the same hue, the four color rule, and 10 different hues but none of them seem to bring a cohesive theme to the design. Is there a solution using color combinations? If not what are good alternatives?
Maybe avoid trying to convey this information using colours, after about three or four, the differentiation/punch of using colours is diluted (and this dilution starts to creep in when you've been designing too long and could stand to reassess assumptions).
Focus on what the colours are meant to 'do' in a more precise way. What differentiates each item on the timeline? Could imagery/icons perhaps on the 'type' of event or duration or any differentiating factor be the real solution to this design/communication problem? Just using colours to 'be colourful' doesn't help you communicate anything. I say for the moment, lose all the colours and reintroduce only when you can justify their existence.
If that doesn't make a lot of sense for the context, sometimes blurred (or semi-blurred) images can serve to add an interesting enough background for certain designs. Again, I would think about how many you use and if they are justified based on the logic above.
Google's Material palette is typically easy to combine. The problem may be that, if the rest of your app/site has a more limited or muted palette, it is going to be hard to introduce 10 colors without it looking strange. In that case, maybe explore using shape or icons to do the differentiating.