Especially in light of your last comment I wonder if the main culprit is light. I have a Rhyncholaelia digbyana which grows, roots, and looks great but won't bloom in my house because I don't have a spot bright enough for it.

I am also still concerned by your fertilizing. Orchids prefer too little fertilizer over too much, and too much can absolutely interfere with blooming. The label directions might say they are for a more dilute solution, but I would still quarter the amount. The plants will still absorb what they need.

Finally, you don't need to change fertilizers seasonally or by growth cycle, and especially to use a bloom booster. Bloom boosters are one of the more fraudulent formulations companies have devised - I'd put it in a lower spot but on the same list as the person who thought of "just add ice" orchids. You really can use one type of fertilizer all year; orchids absorb and store what they need and then use it when growth needs call for it.

It sounds to me like you're doing all the right things. About the only thing that I can think of would be supplemental light during the winter if you can manage it.

There is a previous orchidboard post which details the specific cultural requirements necessary to grow & flower Cattleya Walkeriana. I've posted the link below. You might find this info helpful:

C walkeriana - Tips for Growing & Blooming

Bloom boosters are one of the more fraudulent formulations companies have devised - I'd put it in a lower spot but on the same list as the person who thought of "just add ice" orchids.

Thanks for that!!!

Back to light and window panes. I grow on Canary Islands, so I have plenty of sun if I want to and most of my plants need shade. If I take e.g. Brassavola, a light-hungry plant indoors, the dark green suffused with deep magenta will turn green without any red and without spots. And the window is a south-east oriented window, so it gets full sun, too. If I leave the same plant outside under shade-cloth, it will nearly return to full-sun colour. So, there must be something that does not penetrate (sufficiently) the window panes (UV and ?) Btw, the maximum leaf coloration is the combination low tº and sun. (Something rare over here but I try to avoid for it is plain stress for the plants.)
Your plant looks very nice and healthy to me. Old orchid culture books advice' on reluctant bloomers always is 'starve them' or 'hanging right under the GH-roof' - less nutrients and maximum light. I would add, try to give them outside lights and try to give them a few days of more night drop in tº.

Alas, there are plants that don't want to bloom. In my case a Stanhopea and a P. Moustache.

Just want to ask if anybody knows why this happens..

Every time a new p-bulb is reaches full size the papery cover around it turns this bright pink colour. It keeps its colour for only a couple of days and then what seems like over night, turns back to the usual dull colour.

Is there anything to learn from this? Or is it just what they do?

Anthocyanins?

This is normal, many Cattleya and their hybrids do it and even some Dendrobium.

Is it not an indication of anything? For example it happens as it reaches maturity or that it happens when the p-bulb is has a good reserve of nutrients?

Just seems odd that it changes from white, to pink and back to white again within a week.

C walkeriana needs a good deal more light than most oncidiums...for blooming. It will grow well in less light but you won't see blooms. Increase the light.

I just don't know how to offer it more light, unless a supplement with artificial. It's annoying because here are people that live in the same county as me that have great success with walkeriana!

Should I just try to bombard it with as much light as I can all year?

Or offer it a shadier spot in summer still?